Acta Geologica Academiae Scientiarum Hungaricae, Tomus

Acta Geologica Academiae Scientiarum Hungaricae, Tomus 18, (3-4) pp. 465-480 (1974)

INVESTIGATION OF THE ALKALI FELDSP ARPOLYMORPHS OF THE HUNGARIAN

. .

GRANITOID ROCKS

By

Gy. BUDA

DEPARTMENT OF MINERALOGY, EÖTVÖS L. UNIVERSITY, BUDAPEST

The most important factors influericing the formation of potassium feldsparpolymorphs are the temperature of crystallization, presence of volatile fluxes, sodiumcontent in solid solution, cooling rate, age of formation and bulk chemical compositionof the enclosing rock. The eventual identity of the K-feldspar is controlled by the ratioof the above-mentioned factors. In the granitoid rocks of Hungary two K feldsparpolymorphs have been distinguished. In the granodiorites of South Hungary the por-phyroblastic microclines are frequent, without any relation between their chemicalcompositions and the bulk compositions of the rock. These are crystallized at lowertemperatures from volatile-rich solutions due to the process of potash metasomatism.The other variety is the orthoclase which is the characteristic rock-forming mineral ofthe granite batholiths intruded along the Velence-Balaton fault zone. A positive corre-lation has been found between the bulk compositions of the rock and of the potashfeldspar. They crystallized from the melt at high temperatures during the norm alcourse of mag ma tic evolution.

Geologic setting

The aIk ali feldspars of the granitoid rocks of the Mecsek and VelenceMountains were investigated by X-ray, opticaI and chemical methods to eIu ci-

date the conditions of their formation. Detailed geological-petrological works

have been published on the granitoid rocks of Hungary (JANTSKY, 1957;NAGY, 1967; BUDA, 1969) but a short summary will be given here.

In Hungary there are two granitoid regions:

1. The synkinematic and late-kinematic . anatexite and potash-metaso-matic granitoids occur in the zone of the Mecsek Mountains and Danuhe- Tisza

InterfIuve in the southern part of Hungary. The anatexitic granitoids are con-

formahle with the metamorphic rocks belonging to the amphibolite facies.

These granitoids can be divided into three subgroups on the basis of mineralog-ical and chemical investigations.

1. The metabasites - mainly amphibolite enclaves - are rich in amphi-bole, biotite and plagioclase of relatively high anorthite content (An35)' Por-

phyroblastic microclines are very rare and occur as secondary minerals. As aresult of potash metasomatism the amphiboles were biotitized, the plagioclaseswere sericitized and saussuritized.

2. In the Mecsek Mountains and its surroundings two kinds of porphyro-blastic granodiorites can be distinguished:

Acta Geologica Academiae Scientiarum Hungaricae 18, 1974

466 BUDA, GY.

a) white porphyrohlastic microclinic granodiorite rich in hiotite and

the plagioclase composition An29'

h) red porphyrohlastic microclinic granodiorites cont ain less hiotite,

its plagioclases are rich in alhite (An2S) and have more ordered structure statesas compared to the ahove-mentioned variety.

In hoth types the simple plagioclase twins are predominant. These rocks

were formed hy anatexis and potash metasomatism having foIlowed the region-

al metamorphism.. 3. Late-kinematic granites occur as uncomformahle dykes and smaIl

hatholiths in the synkinematic granodiorite, pinkish in colour, fine-grained,

aplitic or pegmatitic, with less hiotite. Their plagioclases are poor in An (An24)'The cross-hatched microcline pseudomorphs after plagioclase are frequent.

These formed as a result of potash metasomatism along the fault linesof synkinematic granodiorite.

II. Postkinematic quartz-diorites and granites form discordant hatholiths

intruded along the Balaton-Velence fault zone. Detailed investigations haveheen carried out only in the granites and pegmatites of the Velence Mountains.The main constituents are sometimes idiomorphic quartz, orthoclase, plagio-

clase and hiotite. The plagioclase is characterized hy An30 on the average, hy

complex twinning and the ordering of Al/Si is of medium degree. The apliticveins and pegmatitic nests are frequent in the granite. The quartz-dioriteoccurs as enclaves in granite outcrops and has he en struck in horeholes alongthe fault zone.

The investigated potash feldspars were selected from the hasic enclaves

of the Mecsek Mountains, i.e. from the white and red porphyroblastic micro-clinic granodiorite, from the late-kinematic granite and pegmatite, as weIl as

from the granite and pegmatite of the Velence Mountains.

Analytical procedure

a) OpticaI procedures: the optic axial angles were measured from orientedthin sections conoscopically with universal stage. The orientation has heen

compared to the (001) and (010) cleavages measured by reflexion goniometer.

Because of the changing of 2 V in one potash feldspar crystal, several measure-ments were performed.

b) X-ray procedures: two kinds of sample preparation were applied:

1. the monocrystal porphyrohlasts were separated hy hand-picking method,

then they were ground, magnetic minerals removed hy isodynamic magneticseparator. Sometimes heavy liquids were used. 2. The whole rock was ground,

sieved hy a fine wire-gauze of 0.1 mm, washed with water and separated hymeans of magnetic separator.

Acla Geologica Academiae Scientiarum Hungaricae 18, 1974

INVESTlGATION OF ALKALI FELDSPAR POLYMORPHS 467

The finely ground feldspar was mixed with NaCl as a standard. Its peaksoccurring at 28 = 31.38° and 28 = 45.44° were used for corrections. The recordwas made by Phillips,and Siemens X-ray diffractometers, the running condi-tions were as follows: CuK" radiation, 0.5°/min goniometer and 1 cm/min chartspeed, 2 X 10s sec sensitivity, 1° source aperture, 0.1 mm detector aperture,

Ni filter, K. V. 45 in the range between 4° to 48° 28. Having done the required

corrections, the (130) and (131) peaks were checked and if these were single

and sharp, the patterns were regarded as monoclinic, if (131) and (130) weresp lit into (131) (131) and (130) (130), the potash feldspar was considered to betriclinic. The reflections of definite indices based on the tables of WRIGHT and

STEWART, (1968) and corresponding to the A, B qualification of ORVILLE

(1967), were used in the unit-cell parameters compution with the cell-param-

eters refining fixed-index computer program (EVANS et at, 1963). The de-

termination of the unit-cell parameters was carried out on the basis of 8 to18 reflexions. The 21 samples evaluated were chosen from 50 feldspar speci-mens. Selection was carried out on the hasis of the standard deviations

of the cell parameters. The large standard deviations seem to be due to several

factors but the most significant effect is caused by the domain structures

observable even optically (WRIGHT and STEWART, 1968).

c) Chemical analyses: major elements of the feldspars were determinedby "standard" chemical methods and Fe20S' Ti02, MnO, N~O, K20 and P20s

content by instrumental methods the BaO and SrO content by spectral anal-

yses, in the Chemical Laboratory of MÁFI. Analyses were calculated on thebasis of 32(0), using the compuier program described by JACKSON et al. (1967).

Out of the 26 analyses 20 were chosen, where in the X-group the cation pumber

exceeded 3.64, the others were neglected considering that the lack of cations ofgreater extent could be attrlbuted to other mineral inclusions of non-alkali

feldspar structure.

Analytical results

1. Alkali feldspars of the synkinematic and late-kinematic anatexite and

potash metasomatic granodiorites:

1. The microcline of the basic enclaves (Mecsek Mountains: Mórágy) isporphyroblastic, white, cross-hatched, slightly perthitic and contains sericitic

plagioclase, biotite and quartz inclusions. Its average composition: Or7S.8Áb21.5Ano (the analysis is uncertain because of the several inclusions). It has

definite triclinic structure, because (131) and (131) reflexions are sharp andfairly separated from each other. The observed triclinicity is 0.786 (Table 1).

2. Microcline of the porphyroblastic granodiorites:a) White, porphyroblastic microcline (surficial samples of the Mecsek

Mountains: 22.2 A, 16/4,22/2 B; Mórágy, Fazekasboda, Erdósmecske, V éménd).

The cross-hatched twinning cannot be observed, is slightly perthitic and contains

17 Acla Geologjea Academiae Scientiarum Hungaricae 18, 1974

468 BUDA, GY.

Table 1

Unit-cell parameters, triclinicities and optic axial

Á Á Á\

'"Occurrence

I

~o. of

I

linesused

a b c

min.

Unit cell parameters, tiiclinites and optic axial angles of microclines from Mecsek Mountains

22.2 AI

15 I 8.5921IO.00821

12.9650IO.0246 7.2189IO.0018\

90 33.42I1.53

16/4 19 8.5755IO.0045 12.9731 IO.0138 7.2180IO.0004 90 38.67 IO.09

22/2 B 13 8.6129IO.0065 12.9737IO.0220 7.2193IO.0013 90 33.21IO.97

Mórágy 18 8.5797IO.0061 12.9607IO.0260 7.2151IO.0003 90 34.50I1.38Fazekasboda 16

I

8.5922+0.0060 12.9773+0.0355 7.2304+0.0021 90 33.17+1.32

Mórágy (enclave) 16 8.6029~0.0077 12.9693~0.031917.2128~0.0015 90 38.10~1.49

Max. microcline

(MACKENZIE,

1954) 8.574 12.981 7.222 90 41

Max. microcline

(Pellotsalo,

granite, BROWN

1964) 8.560 12.964 7.215 90 39

R = uncertain

strongly sericitic plagioclase, biotite and quartz inclusions. Its average compo-

sition: Ur80.2 Ab18.2 An1.6 (Table II). The (131) and (131), resp. (130) and (130)

reflexions can be fairly separated, indicating triclinic struc_ture. The observedaverage triclinicity is 0.893 (Table 1), the average 2V", is 82°.

Acta Geologica Acadewiae Scientiarum Hungaricae 18, 1974

Porphyroblastic red microclines

2/1 15 8.6005 IO.0068 12.9707 IO.0144 7.2257 IO.0023 90 33.02I1.37

9 14 8.5981 IO.0055 12.9752IO.0169 7.2242IO.0018 90 30.99I1.10

2/1 18 8.5715IO.0031 12.9800IO.0067 7.2293IO.0029 90 41.21 I1.07

7/1 13 8.6049 IO.0020 12.9937 IO.0161 7.2277IO.00I0 90 35.27IO.82

Bátaszék 274.1 m 8 8.5883 IO.0059 12.9865IO.0213 7.2251 IO.0018 90 17.83I1.49

Microclines from aplites

Véménd (2.0/2)

(aplite)

I 9\8.6156+0.0042112.9694+0.026517.2126+0.0015\90 25.21+1.28Véménd (aplite) 10 8.5773IO.0029 12.9701IO.0085 7.2151IO.0013 90 38.04IO.60

Véménd (peg-

matite)I 15 I 8.5997IO.0033 1 12.9828IO.0159 1 7.2148IO.00I0 I 90 28.02IO.90

Standard

INVESTIGATION OF ALKALI F'EI,DPAR POLYMOGPHS 469

115 59 87 30, 1.0000

115 50 87 42 I-I

b) Regarding the occurrences of the red porphyroblastic microclines aredivided into two groups:

IX) Surficial occurrence of the Mecsek Mountains (Samples: 12[1, 19, 22/1

Kismórágy 6/2, Véménd 9/1, Véménd 17/1, Fazekasboda 15/6). The cross-

17* Acta Geologica Academiae Scientiarum Hungarieae 18. 1974

angles of micToclines from l\fecsek Mountains

{JI-

I

V

I

LJ

I

LJ s

I

calcu- observed c-o 2Vo",deg min. I deg, min, (Áj' I lated

Porphyroblastic white microclines from synkinematic granodiorites

115 55.86:!::0.31 187 45.22:!::3.82 I 722.62:!::0.00I 0.97950.9799

I - 0.0004 I

80

115 51.59:!::0.26 87 47.41:!::2.64 722.05:!::0.00 0.9099 0.9095 + 0.0004 84

U5 59.25:!::0.35 87 53.35:!::2.45 724.62:!::0.00 0.9019 0.8580R +0.0439

U5 5c;i.12:!::0.21 87 54.43:!::3.34 721.02:!::0.00 0.8768 0.8819-0.0051 I

79.5

115 58.65:!::0.19

87 56.68:!::3.131 724.29:!::0.00

0.8705 I0.8351

+0.03541

82-86

U5 52.21 :!::0.22 87 55.08:!::3.62723.63:!::0.000.8315 I

0.7860 +0.0455 -

from synkinem atic granodiorites

115 54.34:!::0.42 87 53.00:!::3.37 724.56:!::0.06 0.9073 0.8340

I +0.0733

84

U5 46.10:!::0.33 87 56.78:!::2.73 725.32:!::0.00 0.8904 0.8879 +0.0025 76-81.5

115 56.28:!::0.25 87 47.19:!::2.75 722.27 :!::0.07 0.8794 0.8603 +0.0191 74

115 26.30:!::0.29 87 51.12:!::1.98 729.26:!::0.01 0.8750 0.8591 +0.0159 79

U6 0.17:!::0.11 89 5.15:!::3.48 724.17:!::0.01 0.3545 0.0000 +0.3545 59.5-70

and pegmatites1

115 55.28:!::0.24 78 44.24:!::3.20 724.25:!::0.02.

1.0756 I 1.03R I +0045115 58.53:!::0.13 87 48.76:!::1.45 721.04:!::0.08 0.8960 76

115 46.65:!::0.27 87 59.10:!::2.20 724.90:!::0.00 I 0.8984 I 0.8363R I +0.0621

microclines

Explanation of Table 2: 1. White microcline from Erdosmecske. 2. white microcline fromVéménd (16/4). 3. Red microcline from Kismórágy (6/2). 4. Red microcline from Véménd (9/1 );5. Red microclinefrom Véménd (17/1). 6. Red microcline from Fazekasboda (15/6). 7. Red mi-

Acta' Geologica Academiae Scientiarum Hungaricae 18, 1974

470 BUDA, GY.

Table II

Chemical analyses Of microlines from the synkimenatic

3I

4

Si02 65.67 65.38 65.50.

1

65.54Ti02 0.01 0.01 0.06 0.00

. Al203 18.21 18.13 18.06 18.20Fe203 0.17 0.32 0.16 0.30FeO 0.09 0.09 0.10 0.09MnO 0.02 0.01 0.05 0.01MgO trace 0.14 0.18 0.18CaO 0.40 0.20 0.50 0.15SrO 0.95 1.18 0.89 0.90BaO 0.50 0.58 0.48 0.49Na20 1.96 1.75 1.91 1.76K20

I

11.58 11.71

I

12.00 11.95

P205 0.04 0.03 0.02 0.03CO2 0.05 trace

I

0.24 0.00

H2O-

I

0.00 0.06 0.05

I

0.01

H2O+ 0.28 0.25 0.23 0.23

TotalI

99.83 99.84

1

100.43I

99.84I I

Number of Ions on

Si 12.057 12.040 12.046 12.043Al{v 3.943 3.935 3.914 3.942AlV{ 0.003 0.000 0.000 0.000FeH 0.024 0.044 0.022 0.042Ti 0.001 0.001 0.008Mg - 0.038 0.049 0.049Fe2+ 0.014 0.014 0.015 0.014Mn 0.003 0.002 0.008 0.002Ca 0.067 0.040 0.037 0.029Sr 0.101 0.126 0.095 0.096Ba 0.036 0.042 0.035 0.035Na 0.699 0.625 0.681 0.627K 2.176 2.751 2.815 2.801Z 16.03 16,02 15.98 16.03X 3.64 3.64 3.74 3.65

Molecular

Or

I

78.93

I

81.41

I

80.57 81.86Ab 19.12 17.41 18.35 17.27An 1.95 1.18 1.08 0.87

Cation

Al Si 0.327 0.327 0.325 0.327Al/K+Na 1.555 1.666 1.120 1.150K 78.01 80.55 79.67 81.01Na 20.07 18.29 19.27 18.13Ca 1.92 1.16 1.06 0.86

INVESTIGATION OF ALKALI FELDSPAR POLYMORPHS 471

porphyroblastic granodiorite of Mecsek mountains

I

6 I 7 I 8 I 9

65.58I

65.09 66.47I

65.95 67.110.00 0.01 0.04 0.38 0.35

17.58

I

18.13 17.80

I

16.57 16.320.57 0.39 0.65. 0.00 0.320.09 0.12 0.13 0.28 0.140.01 0.08 0.01

I

trace0.11 0.12 0.24 0.000.55 0.54 0.32 0.81 0.511.54 1.09 1.040.80 0.54 0.381.65 1.95 5.15 3.78 I 3.42

11.65 11.15 6.75 10.10

I

10.300.04 0.11 0.10 0.05 0.030.05 0.05 trace 0.10 0.170.08 0.16 0.00 - I 0.170.37 0.36 0.44 0.37 I 0.47I

100.67 I 99.89 99.52 98.39(?)I

99.30

the basis of 32 (O)12.068 12.012 12.081 12.211 12.3233.813 3.943 3.813 3.616 3.5320.000 0.000 0.000 0.000 0.0000.079 0.054 0.089 0.000 0.044

0.001 0.006 0.053 0.0480.030 0.033 0.0650.014 0.019 0.020 I 0.043 I 0.0220.002 0.013 0.0020.097 0.095 0.062 I 0.13'; I 0.0570.164 0.117 0.1090.058 0.039 0.0270.589 0.698 1.815 1.357 1.2182.735 2.625 1.565 . 2.385 2.413

15.96 16.01 15.99 15.88 15.863.69 3.64 3.67 3.97 3.80

Hatios

80,78

I

77.70

I

46.91 63.09

I

66.6916.37 19.48 51.23 33.82 31.732.85 2.82 1.86 3.09 1.58

Ratios

0.316 0.328 0.316

I

0.296 0.2871.147 1.187 1.128 0.966 0.973

79.96 76.80 45.47 615.2 65.4317.21 20.42 52.72 35.00 33.02

2.82 2.78 1.81 3.48 1.55

crocline from Bátaszék (304.4- 304.8); 8. Red microcline from Pörböly; 9. Red orthoclase fromMágócs (300).

Analysed by G. CSAJÁGHY,K. GUZY.

Acta GeologicaAcademiae Scientiarum Hungaricoe 18, 1974

472 BUDA, GY.

hatched-twinning is not frequent, it is slightly perthitic with frequent qual.tz,chlorite and plagioclase inclusions. Its average composition: OrSO'2Ah17'9Anr9(Tahle II). The reflexions (131) and (131) can he, hut (130) and (130) sometimescannot he separated. The ohserved average triclinicity is 0.860. The alhite insolid solution is less than in the white microcline (Fig. 1). The average of 2V"is 75° (Tahle 1). The two kinds of colours are connected with the different FeH:the ferri content is smalIer in the white microcline (0.034) and greater in thered one (O.Q49) (data concern 32 oxygens).

Co.7267.25

:7.247.237.227217207.197.187.17

7. /6 töw .7.15 r albite7.147.137.127; 117.10

11)2 (;]3 oA4 ..

g~p7 .

. e ",e{\e'"<p0\Ó\{\

. "\e -r.\~'{\.""" Yi\~'{\ 0.'<;)\

High albite

bO

Fig. 1. Unit cell dimensions bo'co plots of alkali feldspars of Hungarian granitoids. 1. Por-phyroblastic white alkali feldspars (Mecsek Mts); 2. Porphyroblastic red alkali feldspars (MecsekMts); 3. Late-kinematic alkali feldspars (Mecsek Mts);' 4. Average (Mecsek Mts); 5. Alkalifeldspars (Velence Mts); 6. Pegmatitic alkali feldspars (Velence Mts); 7. Average (Velence

Mts)

{J) Borehllle samples around the Mecsek-Mts (Bátaszék, Pörhöly, Mágocs).The potash feldspar is porphyrohlastic, cross-hatched and coarse perthitic.The plagioclase and chlorite inclusions are frequent and smalI hematite flakescan also he frequently found. The composition is Or5S.9Ah3S.9An2.2(Tahle II).The (130) and (1~1) reflexions are hroadening, not splitting as an indicationof a disordered structure. Calculated triclinicity = 0.355 (Bátaszék, Tahle 1).2V" varies hetween 59° and 70°.

The groundmass microclines of the granitoids of the Mecsek Mountainsare cross-hatched,justwithout exception and theirtriclinicity isless (LI = 0.50)than those of porphyrohlastic appearance.

3. Late-kinematic granitoids: the microcline (Mecsek Mountains:Véménd) of the microgranite (aplite) is cross-hatched, perthitic. The microclinereplaced plagioclases are frequent. The triclinic structure can he determined

Acla Geologica Academiae Scientiarum Hungarica. 18, 1974


only on the hasis of the (131) and (131) reflexions, hecause (130) and (130)peaks are influenced hy the perthitic alhite. Average triclinicity = 0.986(Tahle 1). The microcline of the pegmatite (Mecsek Mountains: Véménd) iscross-hatched with inclusions and less perthitic albite. The average of the oh-served and calculated triclinicity is 0.867 (Tahle 1).

II. The orthoclases of the post-kinematic granite (Velence Mountains)are homogeneous, without inclusions, slightly perthitic, their composition isOr6S.5Ah2s.2An3.3 (Tahle IV). The (130) and (131) reflexions are sharp, notsplitting which indicates a disordered structure (L1hc = 0.85). The optic axialangle lies between - 560 and - 680, with only one exception (Tahles III and IV).

h) The orthoclases of the pegmatite (Velence Mountains) are free ofperthite, resp. are slightly perthitic. Their composition: Orn.6 Ah21.6Ano.s(Table Ill). The (130) and (131) reflexions are sharp (L1hc = 0.87). The opticaxial angle varies hetween -570 and -600 (Tahles III and IV). On the hasis ofthe optic and X-ray data it has more ordered structure than the orthoclaseof the granite.

Relation between the chemical composition of the

alkali feldspars and of the granitoid rocks. .

In the Mecsek Mountains and in its surroundings, metahasite, grano-

diorite and granite suhgroups have heen distinguished on the hasis of the sumof Ah + Or + Q molecular norms. The feldspar norms of the metahasites

(Or + Ah + Q = 70%): Or4?6 Ah35.1 Anlt.3' The feldspar norms of the por-

phyrohlastic granodiorite (Or + Ah + Q = 70-80%) occurring in a largearea: Or45.2Ah41.4AnI3.4' The norms of the granites resp. granodiorites of the

surroundings of Mecsek Mts.: Or50.2 Ah4?4 An2.4' Typical granite (Or + Ah ++ Q < 80%) occurs in the Velence Mountains which can he characterized hy

the Or46.1Ah45.2AnS.? norms. In the granitoid rocks of the Mecsek Mountainsthe change of An and Ah norms are remarkahle: the hasic inclusions are poor

in Ah and rich in An, while the granite is rich in Ah norms. Considerahle change

cannot he determined in the Or norms. When comparing the change in compo-sition of the Ah and An content of potash feldspars with the analogous norms

of the whole rock, a close correlation is ohtained (except in the case of the por-phyrohlastic granodiorite of the Mecsek Mountains) hut such a clear relation-

ship cannot he ohserved in the case of Or (Fig. 2). It can he demonstrated that

with increasing KINa ratio of the rocks, except the synkinematic granitoids,the KIN a ratio of the potash feldspar will also increase.

There is a positive correlation hetween the sodium content of the potashfeldspar and granite of the Velence Mountains. This lelates to the fact that

in the Velence Mountains the potash feldspar crystallized from ameIt, whilethe vorphyrohlastic microclines of the Mecsek Mountains were -originated

Ac.a Geologica Academiae Scien.iarum Hungaricae 18, 1974

474 BUDA, GY.

Table III

Unit-cell parameters, and optic axial angles of orthoclases of the

c

I~Á

7.2085::1::0.0011 90 0.00

7.2019::1::0.0022 90 0.00

7.2110::1::0.0037 90 0.00

7.2014::1::0.0027 90 O.OJ

7.2191 ::1::0.0009 I 90 0.00

PegmatitePákozd

Székesfehérvár

14 8.6000::1::0.0068 12.9960::1::0.0000 7.2112::1::0.0012 90 0.00

aplite quarry II 8.6236::1::0.0091 12.9975::1::0.0000 7.2082::1::0.0045 90 0.00

Standard orthoclase

Orthoclase x

(Spencer "C")

JONES and

TAYLOR 1961 8.562 . 12.996 7.193 90 0.00

R = uncertain

hy potash metasomatism as a result of the re action of the minerals of the

rocks and' of the volatile-rich potassium-hearing solutions at low temper-

atures, partly independently of the chemical composition of the countryrocks. The enrichment of sodium in the granitoids and in the potash feldsparsaround the Mecsek Mts was due to the migration of sodium prior to potassium.

Structural state of potash feldspar

On the hasis of the ahove- mentioned fact the, porphyrohlastic microcline

crystallized under disequilihrium at low temperatures. These are proved by

the ordered structural states of porphyrohlastsand ~he less ordered ground-mass microclines. The alkali feldspar of late-kinematic granite was crystallized

similarly, which is proved by its highlyordered structure state. The potashfeldspars around Mecsek Mts have disordered structures and high sodium

content but geologically belong to the same complex, consequently, neither

the monoclinic symmetry, nor the high Ah concentration can be explained byhigh crystallization temperatures. Sodium migration precedes the potassium

in the granitization processes, thus in the marginal zone of the granitized

Acta Gealagica Academiae Scientiarum Hungaricae 18, 1974

.1...-

ri a

I

bOccurrence lines

used Á Á

Mélyszög B-41 IS 8.5848::1:: 0.0065 13.0141 ::1::0.0000R

1. road cutting 15 8.6052::1::0.0088 13.0147 ::1::0.0000R

Pákozd D-44 II 8.5913 ::1::0.0059 13.0065::1::0.0000R

SukoróQ 18 8.5719::1::0.0047 12.9991 ::1::0.0000RPákozd II 8.6029::1::0.0038 13.0107::1::0.0000R


postkinematic granites and pegmatites from V elence Mountains

116 6.39::1::0.00 I 90 0.00 723.74::1::0.01 60

115 57.28:1:0.00 I 90 0.00 726.45 ::1::0.01 57 80 10 89

116 Ol 90 0.00 719.3

rocks the sodium enriches and the crystallization of the potash feldspar por-

phyroblasts is rapid. These result in a disordered structure with some tricliniccharacter (diffuse (131) reflexion, cross-hatched twinning, changing 2V, etc.)

at lower temperatures. The feldspar of the granite of the Velence Mountains

crystallized during the norm al course of magmatic evolution at higher temper-atures. The cooling rate was relatively slow, thus they became partly ordered

(Fig. 1). The aIk ali feldspar of the pegmatites belonging to the granite batho-lithe is more ordered, due to volatile enrichment during fractional crystallization

(Fig.1).

Conclusions

a) Factors controlling the struct ural state of alkali feld spars

One of the influencing factors is the temperature of crystallization. The

potash feldspar crystallizing from melt is formed at higher temperature

(Velence Mts) than the microclines formed by potash metasomatism from vola-tile-rich solutions (Mecsek Mts), thus the former one is disordered while thelatter one will be of ordered structure. The potash feldspar forming at higher

Acta Geologica Academiae Scientiarum .Hungaricae 18, 1974

fl

Ideg.y mm I

V

I 2V (OOI) I

(OIO)

deg. mm (Á)' N. I W{3 I NAy N. I NA{3 I N'y

116 7.049::1::0.00 90 0.00 723.13 ::1::0.01 74 -

I

- - 88 87 3

116 4.401::1::0.00 90 0.00 724.49::1::0.01 58.6 - - - 90 90 O

116 1.833::1::0.00 90 0.00 724.04::1::0.01 58

85 I

8 84 88 90 3.5

116 1.733::1::0.00 90 0.00 721.04::1::0.77 56 84 6 88 - - -

116 0.66::1::0.00 90 0.00 726.19::1::0.67 - -1-

- - - -I

1. Orthoclas~ from Sukoró (A). 2. Orthoc1asefrom Sukoró (B). 3. Orthoc1asefrom Pákozd.4. Orthoc1asefrom Meleghill. 5. Orthoc1asefrom Gécsi hill. 6. Pegmatitic orthoc1asefrom Pákozd(A). 7. Pegmatitic orthoc1ase from Pákozd (B). 8. Pegmatitic orthoc1ase from Pákozd (C);


= ~.....

476 BUDA, GY.

Table IV

Chemical analyses of orthoclasesfrom postkinematic

]I

I -1 l 2 3

.

Si02 65.99 65.74 65.75 65.85

I

67.43Ti02 0.00 0.01 0.00 . 0.00 0.00Al20a 18.32 18.80 18.56 18.70 17.80Fe20a 0.09 0.11 0.19 0.17 0.17FeO 0.00 0.05 0.21 0.12 0.10MnO 0.00 0.00 0.00 0.01 0.00MgO 0.00 trace 0.00 trace traceCaO 0.44 0.29 1.30 0.70 0.39BaO - - 0.01 0.09Na20 2.71 3.49 3.44 3.08

1

3.08K20 12.24 11.11 9.68 11.23 I 10.76P205 0.00CO2 0.00

I

-

I

0.01H2O- 0.12 0.16 0.10 0.16

I

'0.03H2O+ 0.28 0.31 0.35 0.27 0.53

Total I 100.19 I 100.07 I 99.69 I 100.38

I

100.29

Numbers of ions on

Si 12.041

I

11.975 11.979

1

11.973I

12.200Al1V 3.940 4.025 3.985 4.007 3.796AlV! - I 0.011 -

I

FeH 0.012 I 0.015 0.026 0.023 0.023Ti 0.000 i 0.001 0.000 0.000 0.000Mg 0.000 0.000 0.000 I 0.000 0.000Fe2+ 0.000 0.008 0.032 0.018 0.015Mn 0.000 0.000 0.000 0.002 0.000Ca 0.086 0.057 0.254 0.136 0.076Ba 0.000 0.000 0.007 0.006 0.000Na 0.959 1.233 1.215 1.086 1.080K 2.849 2.582 2.250 2.605 2.483Z

I

15.99 16.03

I

15.99 16.00 16.02X 3.89 3.88 3.76 3.85 3.65

Molecular

Or

I

74.23

I

67.94

I

61.65

I

69.19

I

69.41Ab 23.53 30.57 31.36 27.19 28.47An 2.24 1.49 6.99 3.62 2.12

Cation

Al/Si 0.327 0.336 0.333 0.335 0.331Al/Ka+Na 1.035 1.055 1.150 1.086 1.065K 73.17 66.70 60.50 68.06 68.23Na 24.62 31.84 32.68 28.37 29.69Ca 2.21 1.46 6.82 3.57 2.08

INVESTIGATION OF ALKALI FELDSPAR POLYMOGPHS 477

~ranites, pegmatites of Velence Mts

6 7 8 10 II

9. Pegmatitic orthoclase from Sukoró. 10. Pegmatitic orthoclase from Székesfehérvár old quarry.ll. Pegmatitic orthoclase from Székesfehérvár aplitic quarry. Analysed by G. CSAJÁGHY,L.NEMES, K. GUZY

Acta Geologica Academiae Scientiarum Hungaricoe 18, 1974

,

65.05 65.23 65.09 66.38 65.57 65.250.00 0.00 0.01 0.03 0.00 0.00

18.17 18.48 18.86 18.72 18.40 18.300.27 0.27 0.22 0.15 0.15 0.120.00 0.00 0.01 0.00 0.00 0.000.00 0.00 0.00 trace 0.00 0.000.16 0.08 trace 0.26 0.00 0.08 .

0.10 0.22 0.07 0.14 0.44 0.10- - - - - -

1.99 2.46 2.92 2.69 2.76 1.8513.84 13.02 12.28 10.92 12.04 14.07

- 0.00 0.00 0.00 0.00 0.00- 0.00 0.00 0.00 0.00 0.00

0.29 0.17 0.28 0.14 0.41 0.320.52 0.57 0.28 0.36 0.53 0.41

100.391

100.50 100.02 I 99.79 100.30 100.50

the basis of 32 (O)11.989 11.963 11.934 . 12.057 12.013 12.0013.947 3.995 4.066 3.943 3.973 3.967

0.010 0.064 0;000 0.0000.037 0.037 0.030 0.021 0.021 0.0170.000 0.000 0.001 0.004 0.000 0.0000.044 0.022 0.000 0.070 0.000 0.0220.000 0.000 0.002 0.000 0.000 0.0000.000 0.000 0.000 0.000 0.000 0.0000.020 0.043 0.014 0.027 0.086 0.0200.000 0.000 0.000 0.000 0.000 0.0000.711 0.875 1.038 0.947 0.980 0.6603.254 3.046 2.872 2.530 2.814 3.301

15.97 16.00 16.04I

16.09 16.01 15.984.03 3.99 3.93 3.58 3.88 4.00

Ratios

82.67

1

77.831

74.36 I 73.34 74.20

I

83.71

17.01 21.06 25.30I

25.88 24.34 15.780.32 Lll I 0.34 0.78 1.46 0.51

Ratios

0.329 0.334 0.341 ,0.327 0.331 0.3310.995 1.012 1.040 1.134 1.047 1.002

81.65 76.84 73.20 72.19 72.51 82.9317.85 22.07 26.45 27.03 25.26 16.57

0.50 1.09 0.35 0.78 2.23 0.50

478 BUDA, GY.

An " 102

Fig. 2. FeldsJ'ar variation in the Hungarian granitoids, plotted on part of Ab-Or-An. L Ana-lysed separated feldspar; 2. Feldspar normatives of the analysed whole rocks (strictly,

Ab-Or-An)

Q(o 194020'94 o JO'940 O'93 o 50'93 ° 40'93° 30'

93° 20' ;930 lD' ~930 O' ~92°50' ~92° 40' ;g,cr92° 30' ?:92° 20' ~92°'10' ~92° O' g91°50' t;91°40' 'jE91° 30'91°'20'91° JO'91° O'90° 50'90°40'90° 30'90° 20'90° JO'90° O'89° SO'

Low albile 1o.

~ . 2...

3D

l'1igh. albile

<II..'ji;<II~:oci,L'cnIE

..

~ximum IImicroclone

.'-~~, '<i8-~~);-~~D- I

0,3 02-01",Monbcli noc

a!kali leldspar -~g~~ö~~g~~ÖQ~g~~b~~° ° o' ° ° o o ° o o o o o o o' ° ° o o~~~~rorororororommmmmmaaarorororororororororororororororommm

00

Fig. 3. Unit-cell dimensions oco-Yoplots of alkali feldspars of Hungarian granitoids. L Por-phyroblastic alkali feldspars; 2. Average; 3. Triclinicities


INVESTIGATION OF ALKALI FELDSPAR POLYlIlORPHS 479

temperature is rich in sodium which prevents the subsequent structural order-

ing, consequently the form of higher symmetry will be preserved at lowertemperature (WRIGHT and STEWART, 1967). The other important factor is thecooling rate. In case of rapid cooling the disordered structure remains also at

lower temperature. A further factor is the volatile content, the quantitative

increase of which results in the structural ordering of the potash feldspar.

The orthoclase of the granite of the Velence Mountains is an .appropriate

example which is structurally le ss ordered than the alkali feldspar of thepegmatites crystallizing from the volatile-rich magma. The chemical composi-,tion of the rock also affects the structural arrangement, especially the alkalies

and aluminium. High aluminium content inhibits ordering, the alkalies facil-itate ordering (MARTIN, 1969). Tbis is valid, however, when crystallization

proceeds from a melt, KIM and HUNAHASHI, (1972) suggest that the age of

formation als() influences the ordering. As confirmed by a great number ofmeasurements, the potash fe1dspars of the Precambrian granites are of mostly

ordered structure, while in younger granites the rate of ordering decrease.The eventual Si/Al ordering depends on the ratio of the factors men-

tioned above. E.g., the high sodium content and rapid cooling of the potash

feldspar porphyroblasts of the surrounding of Mecsek Mts resulted a disordered

structure in spite of the lower temperatures of crystallization.

b) Effect of Si/Al ordering on the most importantparametres of potash feldspar

1. The y, f3and Cocell- parametres are most sensitive to the Si/Al ordering.With decreasing bo, triclinicity increases (Figs 1 and 3).

2. With increasing sodium content the ordering of the structure decreaseswithin one polymorphous variety (orthoclase, microcline).

3. There is a positive correlation between the "bulk composition" andao cell. period (with increasing Or content ao also increases).

REFERENCE5

AUGUSTITHIS,5. 5.: Atlas of the Textural Patterns of Granites, Gneisses and Associated RockTypes. Elsevier, 1973.

BORG, 1. Y.-D. K. 5MITH: Calculaied powder patterns. Part II. 5ix potassium feldspars andbarium feldspar. Am. Min., 54, 163-181, 1969.

BUDA, Gy.: Genesis of the granitoid rocks of the Mecsek and Velence mountains on the basis. of the investigation of the feldspars. Acta Geol. Hung.,13, 131-155, 1969.

CROSBY,P.: Composition and structure state of alkali feldspars from charnockitic rocks onWhiteface Mountain, New York, Am. Min., 56, 1788-1811, 1971.

EVANS, H. T., JR.-D. E. ÁPPLEMAN-D. 5. HANDWERKER: The least squares refinement ofcrsytal unit cells with powder diffraction data by an automatic Computer indexingmethod (abst.). Annu. Meet. Amer. Crystallogr. 50C., Cambridge, Mass. Program,42-43, 1963.


480 BUDA, GY.

GUIDOTTI,C.V.-H. H. HERD-C. L.TUTTLE: Compositionand structural state of K feld-spars from K-feldspar+ Sillimanite-grade rocks in north. western Maine, Am. Min., 58,705-716, 1973.

JACKSON, E. D.-R. E. STEVENS-R. W. BOWEN: A computer-based Procedure for DerivingMineral Formulas from Mineral Analyses. GeoI. Surv. Research Chapter C. GeoI. Surv.Prof. Paper, 575-c, C23-C31, 1967.

JANTSKY, B.: Geology of the Velence Mountains. GeoI. Hung., 1957.KERRICK, D. M.: K-feldspar megacrysts from a porphyritic quartz monzonite Central Sierra

Nevada, California. Am. Min., 54, 839-848, 1969.KIM, C. W.-M. HUNAHASHI: Chronological aspects in granites, Lithos, 5, 241-254, 1972.MARTIN, R. F.: The Hydrothermal Synthesis of Low Albite. Contr. Mineral. and Petrol., 23,

323-339, 1969.NAGY, B.: Mineralogical-petrological and geochemical investigation of the granitoid rocks

of Velence Mts. Földt. Közl., 97, 423-436, 1967.ORVILLE, P. M.: Unit-cell parameters of the microcline-Iow albite and the sanidine-high albite

solid solution series. Ain. Min., 52, 55-86, 1967.PARSONS, L-R. BOYD: Distribution of potassium feldspar polymorphs in intrusive sequences.

Min. Mag., 38, 295-311, 1971.STEWART, D. B.-P. H. RIBBE: Structural explanation for variations in alI parameters of

alkali feldspars with Al/Si ordering. Amer. J. Sci., 267-A, 444-462, 1969.VORMA, A.: Alkali feldspars of the Wiborg rapakivi massif in southeastern Finland. Bull.

Com. GeoI. de Finlande, 1971.WRIGHT, T. L.: The alkali feldspars of the Tatoosh pluton in Mount Rainier National Park.

Am. Min., 49, 715-735, 1964.WRIGHT, T. L.: The microcline-orthoclase transformation in the contact aureole of the Eldora

stock, Colorado Am. Min., 52, 117-136, 1967.WRIGHT, T. L.-D. B. STEWART:X-ray and opticai study of alkali feldspar: 1. Determination

of composition and structural state from refined unit-cell parameters and 2V. Am.Min., 53, 38-87, 1968.

113Y4EHl1E ~EJI04HbIX nOJIEBblX llInATOB rPAHI1TOI1):(OB BEHrpl111

Ab. BYAA

Pe310Me

Ba)!(HeHlllHMH tPaKTopaMH, BJIH5IIOLQHMHHa tPOpMHpOBaHHe nOJIHMoptPHbIX MO)J;HtPHKa-I.\HH LQeJIOtJHbIXnOJIeBbIX lllnaTOB, 5IBJI5IIOTC5ITeMnepaTypa tPOpMIfpOBaHH5I nOCJIe)J;HHX, cO)J;ep-)!(aHHe HaTpH5I, BOllle)J;lllerOB CTPYKTYPY MHHepaJIOB, CKOpOCT OCTbIBaHH5I MarMbI, B03paCTtPOpMHpOBaHH5I nopO)J;bI H XHMHtJeCKHH COCTaB B03HHKalOLQeH nopo)J;bI. <1>opMHpoBaHHe TOH HJIH)J;PyroH nOJIHMoptPHOH MO)J;HtPHKaI.\HHOOYCJIOBJIHBaeTC5ICOOTHOllleHHeM$aKTopOB BJIH5IIOLQHXHareHeTIftJeCKHH nporpecc. B rpaHHTOH)J;ax BeHrpHH MO)!(HO BbI)J;eJIHTb )J;Be nOJIHMoptPHbIX pa3-HOBH)J;HOCTHLQeJIOtJHbIXnOJIeBbIX,lllnaTOB. B rpaHHTOH)J;axIO)!(HOHBeHrpHH tJaCTOBCTpetJaIOTC5InoptPHpOOJIaCTOBbIe MHKpOKJIHHbI ynop5l)J;otJeHHoH CTpYKTYPbI, Me)!()J;Y HX XHMHtJeCKHM COCTa-BOMH XHMH3MOMBMeLQalOLQeHnopo)J;bI HeJIb351 oOHapY)!(HTb KaKYIO JIHOO 0)J;H03HatJHYIO B3aHMO-CB5I3b. OHH oopa30BaJIHCb npH nOHH)!(eHHOH TeMnepaType H3 ooraTbIx JIeTYtJHMHKOMnOHeHTaMHpacTBopoB nYTeM KaJIHHHOrO MeTaCOMaT03a. ):(Pyra51 MO)J;HtPHKaI.\HH31'0 - OpTOKJIa3 c HeynOp5l-)J;OtJeHHOHCTPYKTYPOH, npe)J;CTaBJI5IIOLQHHCOOOIOxapaKTepHbIH MHHepaJI rpaHHTOBbIX OaTOJIH-TOB, nO)J;H5IBlllHeC5IB npHnOBepXHOCTHYIO 30HY B)J;OJIbJIHHHH, coe)J;HH5IIOLQeH03epo EaJIaTOHa c03epOM BeJIeHl.\e. Me)!()J;Y COCTaBOMnopo)J;bI H KaJIIfeBbIX nOJIeBbIX lllnaTOB OOHapY)!(HBaeTC5InOJIO)!(IfTeJIbHa51 KOppeJI5II.\IfOHHa51CB5I3b. OpTOKJJa3bI 3TH HMelOTMarMaTHtJeCKoe npOIfCXO)!()J;eHHe; CJIe)J;OBaTeJIbHO, OHH BbIKpnCTaJIJJH3npOBaJIHCb H3 paCnJIaBOB npH nOBbIllleHHOH TeMnepa-Type.

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