GEOLCE Chapter 2.3 ROCK-FORMING MINERALS

Rock-Forming Minerals

Naturally occurring minerals that make up rocks in the Earth’s crust.

Silicates

Minerals composed mainly of silicon and oxygen.

Silicon-Oxygen Tetrahedron

Basic structural unit of silicate minerals.

Quartz

A silicon dioxide mineral widely found in the Earth’s crust.

Feldspar

A group of aluminosilicate minerals containing Ca, Na, or K.

Augite

A pyroxene mineral found in igneous rocks.

Hornblende

An amphibole mineral found in igneous and metamorphic rocks.

Biotite

A dark mica mineral with perfect cleavage.

Muscovite

A light-colored mica mineral.

Calcite

A calcium carbonate mineral common in sedimentary rocks.

Garnet

A group of silicate minerals used as gemstones and abrasives.

Amethyst

Purple to deep violet quartz caused by trace impurities.

Blue Quartz (Dumortierite Quartz)

Quartz with blue coloration due to fibrous inclusions.

Citrine

Yellow to brown quartz formed due to ferric impurities.

Milky Quartz

White quartz caused by fluid inclusions trapped during formation.

Rose Quartz

Pink to light red quartz due to trace elements.

Smoky Quartz

Gray to brown quartz formed by natural irradiation.

Prasiolite

Green quartz formed by natural heating processes.

Chalcedony

Waxy, fibrous quartz.

Carnelian

Reddish-orange chalcedony colored by iron.

Chrysoprase

Green chalcedony colored by nickel.

Heliotrope (Bloodstone)

Dark green chalcedony with red spots.

Agate

Banded, multicolored quartz.

Onyx

Layered chalcedony with parallel bands.

Flint

Dark, hard quartz found in chalk formations.

Chert

Compact sedimentary rock similar to flint.

Jasper

Red or colored granular quartz due to impurities.

Prase

Dull green granular quartz associated with jasper.