Minerals for Mineralogy Lab Final

Quartz (beta) (pseudomorphs) SiO2 Hexagonal
Quartz (alpha) (stable form) SiO2 Trigonal
Chert (jasper and flint) SiO2 Trigonal
Chalcedony (agate) SiO2 Trigonal
Opal SiO2 * nH2O Amorphous

All show conchoidal fracturing
In thin section quarts should have a flash extinction
1st order birefringence color grey-yellow
Low relief in thin section.
Opal is waxy looking more so than chert,
Chert includes jaspers

(K,Na)AlSi3O8

Microcline (plutonic) Triclinic
Orthoclase (both volcanic and plutonic) Monoclinic
Sanidine (volcanic) Monoclinic

NO TWINNING VISIBLE IN HAND SAMPLES

Microcline can show tartan twinning and perthite in thin section

Orthoclase can show perthite but NOT tartan twinning in thin section

Sanidine can NOT show tartan twinning, can NOT show perthite in thin section

(Na,Ca)Al1-2Si3-2O8

Albite (Na) – Anorthite (Ca) Triclinic

CANNOT TELL APART IN HAND SAMPLE

Both shows polysynthetic twinning in hand sample
Albite can have labradorescence in hand sample (labradorite)
Albite has more Sodium
Anorthite has more Calcium

Na Felspathoid

(Na,K)AlSiO4

Hexagonal

NOT FOUND WITH QUARTZ
NO good cleavage
Greasy in hand sample
It looks like quartz or sanidine in thin section.

Mg3Si2O5(OH)4 Mg
Antigorite and Chrysotile
Sheet Silicate
Monoclinic

Super fine grained
Hardness greater than fingernails
Fiberous in thin section
Can be found with Talc
NOT found with Chlorite

Al2Si2O5(OH)4
Clay mineral group
Al Sheet Silicate
Triclinic

Can be found with Feldspar
NO good cleavage
Can be powdery in hand sample or like plaster
Can be scratched with fingernail
Brown blob in thin section

Mg3Si4O10(OH)2
Clay mineral group
Mg Sheet Silicate
Monoclinic

Can be found with serpentine
Has birdseye extinction
Soapy feel in hand sample

Al2Si2O5(OH)4
Clay mineral group
Al Sheet Silicate
Triclinic

Can be found with Feldspar
NO good cleavage
Can be powdery in hand sample or like plaster
Can be scratched with fingernail
Brown blob in thin section