Name And Composition
QUARTZ-SiO2

FELDSPAR

ORTHOCLASE - KalSi3O8
PLAGIOCLASE - NaAlSi3O--CaAl2Si2O

MICA

MUSCOVITE - KAl3Si3O10(OH)2
BIOTITE - K(Mg ,Fe)3AlSi3O10(OH)2

FERROMAGNESIAN MINERALS

HORNBLENDE - Ca2Na(Mg,Fe)4(Al,Fe,Ti)3Si6O22(O,H)2
PYROXENE - Ca(Mg,Fe,Al) (Si,Al)2O6
OLIVINE - (Fe,Mg)2SiO4 

CALCITE - CaCO3

GYPSUM - CaSO4.2H2O

HALITE - NaCl

IGNEOUS ROCKS (Fire-formed Rocks)
Intrusive or Platonic--Formed under ground.

Granite
Rhyolit
Diorite
Gabbro
Andersite
Peridolite
Felsite

Extrusive or Volcanic Rocks

Pumice--a froth of volcanic material.
Tuff--volcanic ash that has consolidated.
Basalt--most abundant of volcanic rocks.
Scoria--a form of basalt with a large number of air holes.

SEDIMENTARY ROCKS (Formed from sediments of other rocks.)

Sandstone--from sand or quartz.
Mudstone--are fine grained rocks--Feldspar is the main mineral.
Shale--are fine grained rocks that slit into slabs--Feldspar.
Limestone--made up chiefly of the mineral calcite CaCO3, that has been deposited by chemical processes.
Chalk--is made up in part of skeletons of microscopic oceanic life.
Dolomite--Dolomite, CaMg(CO3)2 is the main mineral, formed with limestone.
Rock Salt--NaCl or Sodium Chloride is the mineral.

Many sedimentary rocks contain structures that are formed only after the original sediment was deposited. Among these are the nodules, concretions, and geodes.

METAMORPHIC ROCKS (Changed-form rocks.)
Metamorphic rocks are formed from original igneous or sedimentary rocks or other metamorphic rocks. The agents of metamorphism are, heat, pressure, and chemically active fluids.

Slate--produced from Shale.
Phyllite--produced shale--is actually slate that has undergone further metamorphism.
Schist--from many igneous, sedimentary, or lower--grade metamorphic rocks.
Gneiss--igneous rocks such as granite, gabbro or diorite.
Marble--from limestone and dolomite.
Quartzite--from sandstone

NOTE:
Lee Olsen was President of the Wasatch Gem Society in 1983---A teacher with vast knowledge of the earth sciences. This article was printed in our bulletin before and won an award in the contest. He passed away Dec. 3, 1986.