Periclase and Pyrope optical mineralogy

8/19/2019 Periclase and Pyrope optical mineralogy

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Laboratorium Mineralogi & Petrograf2016

PERICLASE

ABOUT PERICLASE

Periclase is a r are but widely distributed mineral.

Formula : MgO Isometric.

RI Value : n = 1.73 to 1.7!".

#olor : #olorless in t$in sections.

Form : Periclase occurs in small crystals or an$edral crystal aggregates.

Indi%idual an$edral may be r ecogni&ed by clea%age tr aces.

#lea%age : #ubic. Parting' dodeca$edral.

Relie( : )ig$' n * balsam.

+ire(ringence : ,il. -ar between crossed nicols.

#$aracter : /$e cubic clea%age' $ig$ r elie(' and isotro0ic c$ar acter ta en toget$er

ar e distincti%e.

lteration : Periclase is usually alter ed to brucite w$ic$' in turn' may be alter ed to

$ydromagnesite.

Occurrence : /$e most common occurr ence o( 0ericlase is in metamor0$ic

limestones. It is (ound as cor es wit$in brucite s0ots t$at ar e (ormed by

$ydr ation o( t$e 0er iclase. rti(icial 0ericlase' now 0r e0ared on a

commercial scale (rom selected magnesite' is mor e (amiliar t$an t$e

natural mineral. It is used as a $ig$2gr ade electrical insulator .

Nama: Danendra GarudaNIM : 111140015Plug : 5


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PYROPE

ABOUT PYROPE

Pyro0e is one o( t$e si minerals o( garnet grou0.

Formula : Mg3b45i"63.

RI Value : n = 1.761 to 1.7!".

#olor : #olorless' 0ale reddis$' 0ale to dar brown' greenis$ gray' in t$in

sections. #rystals are o(ten &oned.

Form : 8u$edral dodeca$edral cr ystals in si2sided sections and

tra0e&o$edral crystals in eig$t2sided sections are common.

#lea%age : bsent.

Relie( : Very $ig$' sur(ace roug$' n * balsam.

+ire(ringence : %arieties are dar between cr ossed nicols but some $a%e wea or %ery

wea bir e(ringence. /$e bire(ringent ar eas are o(ten arranged in &ones

or sectors.

#$aracter : 9arnet resembles s 0incl' but t$e latter occurs in octa$edra. /$e

di((erent inds o( garnet may be determined by indices o( re(raction

combined wit$ t$e determination o( t$e s0eci(ic gr a%ity.

lteration : /$e most common alteration 0roduct o( garnct is c$lorite.



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Occurrence : 9arnet is es 0ecially c$aracteristic o( metamor0$ic mineral. It is also a

%ery common detrital mineral. Pyro0e is 0ractically con(ined to

0eridotites and der i%ed ser0entines.


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Periclase and Pyrope optical mineralogy