TECTOSILICATES

Tectosilicates (framework silicates)

•Name came from the Greek tectron, meaning “builder”.

•The Tectosilicate structure is a three-dimensional network of silica tetrahedra, with each tetrahedral unit sharing all of its four oxygen atoms.

•The largest single group of silicates, and include several rock-forming minerals.

TECTOSILICATE GROUPS

SiO Group

•The SiO2 structure is electrically neutral – it does not require additional cation or anion species.

•SiO2 is quartz in its simplest form.

2

QUARTZ

CHEMICAL COMPOSITION

CRYSTAL SYSTEM

PHYSICAL PROPERTIES

DISTINGUISHIN

G FEATUR

ES

USES

COLOR

HARDNESS

SPECIFIC

GRAVITY

LUSTER FRACTURETENACI

TYSTREAK

SiO2

Hexagonal

Colorless or white

7 2.65 vitreous conchoidal brittle

Colorless or white

Distinguished from calcite by its high hardness

Gemstones, manufacture of glass and silica brick, porcelain and sandpaper

QUARTZ

TRIDYMITE

CHEMICAL COMPOSITION

CRYSTAL SYSTEM

PHYSICAL PROPERTIES

DISTINGUISHING

FEATURESUSES

COLOR

HARDNESS

SPECIFIC

GRAVITY

LUSTER FRACTURETENACI

TYSTREAK

SiO2

Monoclinic/ Orthorhombic-hexagonal

Colorless or white

7 2.26

vitreous

conchoidal

brittle

Colorless or white

Crystalline outline and refractive index

Ceramics

TRIDYMITE

CRYSTALOBALITE

CHEMICAL COMPOSITION

CRYSTAL SYSTEM

PHYSICAL PROPERTIES

DISTINGUISHIN

G FEATUR

ES

USES

COLOR

HARDNESS

SPECIFIC

GRAVITY

LUSTER FRACTURETENACI

TYSTREAK

SiO2

Tetragonal-isometric

Colorless 7 2.32 vitreous conchoid

al brittleColorless or white

Exhibits double refraction, sometimes fluorescent white cream

Ceramics

CRYSTALOBALITE

OPAL

CHEMICAL COMPOSITION

CRYSTAL SYSTEM

PHYSICAL PROPERTIES

DISTINGUISHIN

G FEATUR

ES

USES

COLOR

HARDNESS

SPECIFIC GRAVITY

LUSTER FRACTURETENACITY

STREAK

SiO2

nH2

O

Amorphous

Colorless or white, sometimes it have pale colors because of impurities

5-6

2.25

Vitreous

conchoidal

brittle White

Lesser hardness and specific gravity and by presence of water

Gem

OPAL

JASPER

CHEMICAL COMPOSITION

CRYSTAL SYSTEM

PHYSICAL PROPERTIES

DISTINGUISHIN

G FEATUR

ES

USES

COLOR

HARDNESS

SPECIFIC GRAVITY

LUSTER FRACTURECLEAVAGE

STREAK

SiO2

Hexagonal/trigonal

Red, yellow brown and numerous others

7 2.7 Vitreous

conchoidal

none White

Brick-red to brownish-red contains hematite ; clay to yellowish-white or grey; goethite produces brown or yellow.

Jewelry and ornamentation

JASPER

CHALCEDONY

CHEMICAL COMPOSITION

CRYSTAL SYSTEM

PHYSICAL PROPERTIES

DISTINGUISHIN

G FEATUR

ES

USES

COLOR

HARDNESS

SPECIFIC GRAVITY

LUSTER FRACTURECLEAVAGE

STREAK

SiO2

Hexagonal/trigonal

white 7 2.7 Waxy to dull

conchoidal

none White Relatively

porous ceramics

CHALCEDONY

AGATE

CHEMICAL COMPOSITION

CRYSTAL SYSTEM

PHYSICAL PROPERTIES

DISTINGUISHIN

G FEATUR

ES

USES

COLOR

HARDNESS

SPECIFIC GRAVITY

LUSTER FRACTURETENACITY

STREAK

SiO2Amorphous

Colorless or white, sometimes it have pale colors because of impurities

5-6

2.25

Vitreous

conchoidal

brittle White

Lesser hardness and specific gravity and by presence of water

Gem

AGATE

FELDSPAR GROUP

•A group of aluminosilicate minerals that contain calcium, sodium or potassium.

•The most common minerals on earth’s crust.

•Feldspars are the major component of most igneous rocks.

•There are two groups of feldspars: the ALKALI FELDSPARS and PLAGIOCLASE FELDSPARS.

ALKALI FELDSPARS

•The alkali feldspar group are those feldspar minerals rich in the alkali elements, potassium and sodium.

•Potassium and sodium feldspars are not perfectly miscible in the melt at low temperatures, intermediate compositions of the alkali feldspars therefore occur only in higher temperatures environments

MICROLINE

CHEMICAL COMPOSITION

CRYSTAL SYSTEM

PHYSICAL PROPERTIES

DISTINGUISHING FEATURE

S

USES

COLOR

HARDNESS

SPECIFIC

GRAVITY

LUSTER FRACTURETENACITY

STREAK

KAISi3O8

Triclinic

White to pale yellow

62.54 – 2.57

Vitreous

conchoidal

brittle white

Distinguished from orthoclase by the microcline (“tartan”) twinning

Manufacture of porcelain

MICROLINE

ORTHOCLASE

CHEMICAL COMPOSITION

CRYSTAL SYSTEM

PHYSICAL PROPERTIES

DISTINGUISHING FEATURE

S

USES

COLOR

HARDNESS

SPECIFIC

GRAVITY

LUSTER FRACTURETENACITY

STREAK

KAISi3O8

Monoclinic

White to gray

6 2.57Vitreous, pearly

conchoidal

brittle white

Right angle cleavage and insoluble in acids

Manufacture of porcelain, sometimes in gemstones

ORTHOCLASE

SANIDINE

CHEMICAL COMPOSITION

CRYSTAL SYSTEM

PHYSICAL PROPERTIES

DISTINGUISHING FEATURE

S

USES

COLOR

HARDNESS

SPECIFIC

GRAVITY

LUSTER FRACTURETENACITY

STREAK

(K,Na)AISi3

O8

Monoclinic

colorless 6

2.56 – 2.62

Vitreous, pearly

conchoidal

brittle white

Optic orientation differs from orthoclase and show different types of twinning compared to plagioclase

Ceramics

SANIDINE

ANORTHOCLASE

CHEMICAL COMPOSITION

CRYSTAL SYSTEM

PHYSICAL PROPERTIES

DISTINGUISHING FEATURE

S

USES

COLOR

HARDNESS

SPECIFIC

GRAVITY

LUSTER FRACTURETENACITY

STREAK

(Na,K)AlSi3O

8

triclinic

Colorless to white

6-6.5

2.6 vitreousConchoidal to uneven

brittle white Oblique

cleavageornaments

ANORTHOCLASE

PLAGIOCLASE FELDSPARS

•The series ranges from albite to anorthite endmembers (with respective compositions NaAlSi3O8 to CaAl2Si2O8), where sodium andcalcium atoms can substitute for each other in the mineral's crystal lattice structure.

•Plagioclase in hand samples is often identified by its polysynthetic twinning or 'record-groove' effect.

PLAGIOCLASE FELDSPARS

•The composition of a plagioclase feldspar is typically denoted by its overall fraction of anorthite (%An) or albite (%Ab), and readily determined by measuring the plagioclase crystal's refractive index in crushed grain mounts, or its extinction angle( an optical characteristic and varies with the albite fraction (%Ab)) in thin section under a polarizing microscope. 

ALBITE (%An: 0-10, %Ab: 100-90)

CHEMICAL COMPOSITION

CRYSTAL SYSTEM

PHYSICAL PROPERTIES

DISTINGUISHING FEATURE

S

USES

COLOR

HARDNESS

SPECIFIC

GRAVITY

LUSTER FRACTURETENACITY

STREAK

NaAISi3O8

Triclinic

Colorless, white or gray

6 2.62Vitreous, pearly

subconchoidal

brittle white

Twin striations, insoluble in HCl

Ceramics

ALBITE

OLIGOCLASE (%An: 10-30, %Ab: 90-70)

CHEMICAL COMPOSITION

CRYSTAL SYSTEM

PHYSICAL PROPERTIES

DISTINGUISHING FEATURE

S

USES

COLOR

HARDNESS

SPECIFIC

GRAVITY

LUSTER FRACTURETENACITY

STREAK

(Ca,Na)(Al,Si)4O8

triclinic

Grey, white 6 2.5 vitreous

Conchoidal to uneven

brittle white

Usual habit is massive or granular, does form tabular crystals, commonly twinned

OLIGOCLASE

ANDESINE (%An: 30-50, %Ab: 70-50)

CHEMICAL COMPOSITION

CRYSTAL SYSTEM

PHYSICAL PROPERTIES

DISTINGUISHING FEATURE

S

USES

COLOR

HARDNESS

SPECIFIC

GRAVITY

LUSTER FRACTURECLEAVAGE

STREAK

(Ca,Na)(Al,Si)4O8

triclinic

Grey, white

6-6.5

2.7Subvitreous to pearly

Conchoidal to uneven

perfect white

Exhibits multiple twinning

ANDESINE

LABRADORITE (%An: 50-70, %Ab:50-30)

CHEMICAL COMPOSITION

CRYSTAL SYSTEM

PHYSICAL PROPERTIES

DISTINGUISHING FEATURE

S

USES

COLOR

HARDNESS

SPECIFIC

GRAVITY

LUSTER FRACTURECLEAVAGE

STREAK

(Ca,Na)(Al,Si)4O8

triclinic

Blue, grey, white

6-6.5

2.7 vitreous

Uneven to conchoidal

perfect white

Play of iridescent colors

gemstone

LABRADORITE

ANORTHITE (%An: 90-100, %Ab: 10-0)

CHEMICAL COMPOSITION

CRYSTAL SYSTEM

PHYSICAL PROPERTIES

DISTINGUISHING FEATUR

ES

USES

COLOR

HARDNESS

SPECIFIC

GRAVITY

LUSTER FRACTURETENACITY

STREAK

CaAl2

Si2O

8

Triclinic

colorless 6 2.76 Vitreou

sconchoidal

brittle white

Twin Striations, decomposed in HCl

Ceramics

ANORTHITE

FELDSPATHOID GROUP

Feldspar-like minerals that are deficient in silica content. These are relatively rare and are important in the classification of igneous rocks.

LEUCITE

CHEMICAL COMPOSITION

CRYSTAL SYSTEM

PHYSICAL PROPERTIES

DISTINGUISHING FEATUR

ES

USES

COLOR

HARDNESS

SPECIFIC

GRAVITY

LUSTER FRACTURETENACITY

STREAK

KAlSi2O6

Tetragonal

White to gray

5.5-6

2.47 Vitreous, dull

conchoidal

brittle white

Infusible, trapezohedral form

Fertilizer, artificial alum

LEUCITE

NEPHELINE

CHEMICAL COMPOSITION

CRYSTAL SYSTEM

PHYSICAL PROPERTIES

DISTINGUISHING FEATURE

S

USES

COLORHARDNESS

SPECIFIC

GRAVITY

LUSTER FRACTURETENACITY

STREAK

(Na,K)AlSiO4

Hexagonal

Colorless to yellowish

5.5-6

2.60- 2.65

Vitreous, greasy

subconchoidal

brittle white Gelatinizin

g in acidGlass industry

NEPHELINE

SODALITE

CHEMICAL COMPOSITION

CRYSTAL SYSTEM

PHYSICAL PROPERTIES

DISTINGUISHING FEATURE

S

USES

COLORHARDNESS

SPECIFIC

GRAVITY

LUSTER FRACTURETENACITY

STREAK

Na8Al6Si6

O24Cl

2

Isometric Blue 5.5-

6

2.15- 2.30

Vitreous uneven britt

le white

Soluble in HCl, produces silica jelly when evaporated and its blue color

Ornament

SODALITE

LAZURITE

CHEMICAL COMPOSITION

CRYSTAL SYSTEM

PHYSICAL PROPERTIES

DISTINGUISHING FEATURE

S

USES

COLORHARDNESS

SPECIFIC

GRAVITY

LUSTER FRACTURETENACITY

STREAK

(Na,Ca)8

Al6Si

6O24(S,SO)4

Isometric

Deep Azure-Blue

5-5.5

2.40- 2.45

Vitreous, greasy

uneven brittle blue

Blue color and presence of associated pyrite

Lapis Lazuli-high prized ornament stone

LAZURITE

PETALITE

CHEMICAL COMPOSITION

CRYSTAL SYSTEM

PHYSICAL PROPERTIES

DISTINGUISHING FEATURE

S

USES

COLORHARDNESS

SPECIFIC

GRAVITY

LUSTER FRACTURETENACITY

STREAK

Li(AlSi4O1

0)

Monoclinic

Colorless to gray

6-6.5 2.4

Vitreous, pearly

uneven brittle white Platy habit,

InsolubleOre of lithium

PETALITE

SCAPOLITE SERIES

The scapolites (Gr. asairos, rod, stone) are a group of rock-forming silicate minerals composed of aluminium, calcium, and sodium silicate with chlorine, carbonate and sulfate. The two endmembers are meionite (Ca4Al6Si6O24CO3) and marialite (Na4Al3Si9O24Cl).

MARIALITE

CHEMICAL COMPOSITION

CRYSTAL SYSTEM

PHYSICAL PROPERTIES

DISTINGUISHING FEATURE

S

USES

COLORHARDNESS

SPECIFIC

GRAVITY

LUSTER FRACTURETENACITY

STREAK

Na4(Al3Si

9O24)Cl

Tetragonal

White to gray

5-62.55- 2.74

Vitreous

conchoidal

brittle white

Fibrous appearance on the cleavage surface

Gemstone

MARIALITE

MEIONITE

CHEMICAL COMPOSITION

CRYSTAL SYSTEM

PHYSICAL PROPERTIES

DISTINGUISHING FEATURE

S

USES

COLORHARDNESS

SPECIFIC

GRAVITY

LUSTER FRACTURETENACITY

STREAK

Ca4(Al6Si

9O24)(CO3)

Tetragonal

White to gray

5-62.55- 2.74

Vitreous, dull

conchoidal

brittle white

Fibrous appearance on the cleavage surface

Gemstone

MEIONITE

ANALCIME

CHEMICAL COMPOSITION

CRYSTAL SYSTEM

PHYSICAL PROPERTIES

DISTINGUISHING FEATURE

S

USES

COLORHARDNESS

SPECIFIC

GRAVITY

LUSTER FRACTURETENACITY

STREAK

NaAlSi2O6

H2O

Isometric

White or colorless

5-5.5 2.27 Vitreo

usconchoidal

brittle white

Gives water in the closed tube, free growing crystals

For building materials

ANALCIME

ZEOLITE SERIES

These are hydrous Ca and Na tectosilicates, which have Al present in both tetrahedral and octahedral sites.

The name is derived from the fact that when you fuse ground up mineral, it swells. Zeo means boil and lite means stone (from the Greek).

NATROLITE

CHEMICAL COMPOSITION

CRYSTAL SYSTEM

PHYSICAL PROPERTIES

DISTINGUISHING FEATURE

S

USES

COLORHARDNESS

SPECIFIC

GRAVITY

LUSTER FRACTURETENACITY

STREAK

Na2Al2Si3O10-2H2

O

Orthorhombic

White or colorless

5-5.5 2.25 Vitreo

us

Uneven-conchoidal

brittle white

Gives water in the closed tube, and gelatinizes upon evaporation

Ornament

NATROLITE

CHABAZITE

CHEMICAL COMPOSITION

CRYSTAL SYSTEM

PHYSICAL PROPERTIES

DISTINGUISHING FEATURE

S

USES

COLORHARDNESS

SPECIFIC

GRAVITY

LUSTER FRACTURETENACITY

STREAK

Ca2Al2Si4O12 - 6H2

O

Hexagonal

White or colorless

4-52.05-2.15

Vitreous uneven britt

le white Rhombohedral crystals Ornament

CHABAZITE

HEULANDITE

CHEMICAL COMPOSITION

CRYSTAL SYSTEM

PHYSICAL PROPERTIES

DISTINGUISHING FEATURE

S

USES

COLORHARDNESS

SPECIFIC

GRAVITY

LUSTER FRACTURETENACITY

STREAK

(Ca,Na)2-

3Al3(Al,Si)2Si13

O36 · 12H2

O

Monoclinic

White or colorless, yellow, or red

3.5-4

2.18-2.2

Vitreous, pearly

conchoidal

brittle white

Gives water in the closed tube, one direction of perfect cleavage

Ornament

HEULANDITE

STILBITE

CHEMICAL COMPOSITION

CRYSTAL SYSTEM

PHYSICAL PROPERTIES

DISTINGUISHING FEATURE

S

USES

COLORHARDNESS

SPECIFIC

GRAVITY

LUSTER FRACTURETENACITY

STREAK

 CaAl2Si7

O18 · 7(H2

O)

Monoclinic

White

3.5-4

2.1-2.2

Vitreous, pearly

uneven brittle

colorless

Pearly luster on cleavage part, sheaflike group of crystals

Ornament

STILBITE