Earth Science Mineral and Rock Identification

Magnetite

Blackish or grey

magnetic

metallic

Sulfur

Yellow

smelly

usually large

Muscovite

Light colored mica

sheets peel away (one plane of cleavage)

Biotite

Dark mica

sheets peel away (1 plane of cleavage)

Galena

Silver

metallic

cubic cleavage

very heavy

Pyrite

Looks like gold

chunky crystals

Talc

Very soft/slippery

not translucent

leaves residue on fingers when rubbed

Hardness of 1 (fingernail can scratch)

Gypsum

Softer than fingernail

1 strong cleavage

translucent

Calcite

Any color, but usually light

Often translucent

WILL FIZZ

Softer than glass

Hardness of 3 (copper coin can scratch it)

Halite

Translucent

Cubic (3 planes of cleavage)

Salty

Olivine

Lighter green color

Very grainy

Hardness of 7 (can scratch glass)

Chalcopyrite

Brassy/gold color

Finer crystals than pyrite (Gold looks painted on)

Will not scratch glass (hardness of 4)

Quartz

Hardness of 7

No cleavage but conchoidal fractures (curving surfaces)

Glassy

Can be any color, only 1 on the test

Garnet

Reddish purple to brownish red

Hard (7)

Glassy

12 or 24 sided crystals (like tiny soccer balls)

Fluorite

Purple, to clear, to green, to yellow, but purple is the most common

Softer than quartz and glass (H=4)

Will not fizz

Has 4 good cleavage’s

Glassy and translucent

Hematite

Can be rusty red to silvery

Can be metallic or not metallic

Always has a reddish brown streak

Orthoclase feldspar

H=6

Two cleaveges

Reddish brown to white with an internal streakiness or waviness

Albite feldspar

H=7

Two planes of cleavage

White

Labradorite feldspar

H=6

Two planes of cleavage

Usually darkish grey

Visible striations and blue shimmer

Sphalerite

Dark brown

Yellow brown streak on white plate

Slightly metallic

Sulfur like smell when powdered

Augite

Dark green to black

90 degree cleavage angles

Not splintery

Hornblende

Dark green to black

Long crystals

120 degree cleavage angles

Splintery lines on all faces

Pumice

Frothy

Grayish white

Vesicular (filled with holes)

So light it floats

Scoria

Vesicular (has holes)

Brownish red to black

Obsidian

Glassy and dark colored

Conchoidal fracture

Black but not mafic

Phaneritic rocks

Coarse grained

Large visible crystals

Intrusive

Granite

Light colored overall

Can be whitish to pinkish

Will have glassy quartz, feldspars, and black biotite

Felsic

Diorite

Salt and pepper rock (Intermediate)

Has more dark biotite and a little quartz

Gabbro

Mafic

Has lots of hornbblende

Aphanitic rocks

Fine grained

Crystals not visible

Extrusive rocks

Ryolite

Typically pinkish to whiteish

Felsic

Fine grained

Large

Andesite

Typically greyish, brownish, or greenish

Fine grained

Small feldspar or hornblende crystals

May be vesicular

Basalt

Black, grey or greenish black

Fine grained

Unlayered, unfoliated, may be vesicular

Pegmatitic rocks

REALLY large crystals

Very coarse grained

Coal

Feels light

Shiny black

May see plant remains inside

Coquina

Fossiliferous limestone

Shells compacted together (lithified)

Will fizz

Conglomerate

Rounded pebbles dominant clast type

Breccia

Angular clasts (Sharp pebbles) are more dominant

Chalk

Whitish to grey

Can write with it

Very fine grained

Chert

Any color, but often grey or creamy white

Conchoidally fractured surfaces

Shale

Very fine grained

Lithified mud

Smooth feeling

Grey or black toned

Bedded

Sandstone

Feels like sandpaper

Distinctive gritty feel

Can see compacted sand grains

Usually light toned

Arkose

Gritty

Often iron oxidized an rusty appearing

Small feldspar and mica visible

Fossiliferous Limestone

Will fizz

Contains fossils of some sort, often shell or coral

Usually light to brown tones

Slate

Very planar foliage where the rock will split

Any color possible, usually grey, black, reddish or purplish

Dull surfaces

Minerals not visible to the eye

Phyllite

Similar to slate, but foliation is more wavy/wrinkly

Has more of a sheen (light reflects)

Minerals not visible

Schist

Similar to phyllite, but minerals are visible and commonly have glittery micas

Has other chunky metamorphic minerals like garnet

Foliation is commonly wavy

Gneiss

Banded/striped appearance

Can be light or dark toned overall

Minerals are large enough to see

Bands are separated into lighter and darker ones

Augen Gneiss

Type of gneiss that has eye like crystals (augen = eye)

Augen is usually feldspar, but can be garnet

Quartzite

Massive, sugary and frosted texture

Comes from quartz sandstone

Hard, will scratch glass

Will not fizz

Light to pinkish tones usually

Marble

Massive sugary texture

Comes from limestone (calcite)

Softer than glass

Will fizz

Usually whitish to cream, grey to pink

Foliated Rocks

Parallel arrangement of grains that give the rock a striped appearance

Non Foliated Rocks

No clear banding or layering