ER123 Rock & Mineral ID Basic Properties + Photos

Calcite

Mineral; carbonate group; reacts with acid; rhombohedral cleavage; usually clear, white, gray, or honey-colored; softer than quartz.

What mineral reacts strongly with acid and has rhombohedral cleavage?

Calcite.

Halite

Mineral; halide group; cubic cleavage; usually clear, white, or pink; tastes salty if lab allows taste test.

What mineral has cubic cleavage and a salty taste?

Halite.

Quartz

Mineral; silicate group; hard enough to scratch glass; glassy luster; no cleavage; conchoidal fracture.

What mineral is hard, glassy, scratches glass, and has no cleavage?

Quartz.

Gypsum

Mineral; sulfate group; very soft; can be scratched by fingernail; often white, clear, or pearly.

What mineral is very soft and can be scratched by a fingernail?

Gypsum.

Hematite

Mineral; oxide group; reddish-brown streak; may look metallic gray, red, or earthy.

What mineral has a reddish-brown streak?

Hematite.

Biotite

Mineral; mica/silicate group; dark brown-black mica; peels into thin flexible sheets.

What mineral is dark mica that peels into thin sheets?

Biotite.

Galena

Mineral; sulfide group; metallic lead-gray; very dense/heavy; cubic cleavage.

What mineral is metallic gray, very dense, and has cubic cleavage?

Galena.

Hornblende

Mineral; amphibole/silicate group; dark green-black; elongated crystals; cleavage angles around 60/120 degrees.

What dark mineral has elongated crystals and amphibole cleavage around 60/120 degrees?

Hornblende.

Fluorite

Mineral; halide group; often purple, green, clear, or colorful; softer than glass; commonly cubic crystals.

What colorful mineral is softer than glass and often forms cubic crystals?

Fluorite.

Orthoclase

Mineral; feldspar/silicate group; commonly pink, salmon, white, or cream; two cleavage planes; no striations.

What feldspar is often pink or salmon-colored?

Orthoclase.

Pyrite

Mineral; sulfide group; brassy metallic gold color; “fool’s gold”; often cubic crystals.

What mineral is brassy gold and called fool’s gold?

Pyrite.

Plagioclase

Mineral; feldspar/silicate group; usually white, gray, or translucent; may show fine striations; two cleavage planes.

What feldspar is usually white/gray and may show striations?

Plagioclase.

Augite

Mineral; pyroxene/silicate group; dark green-black; blocky/stubby crystals; cleavage close to 90 degrees.

What mineral is dark, blocky, and a pyroxene with cleavage near 90 degrees?

Augite.

Graphite

Mineral; native element; dark gray-black; greasy feel; writes on paper.

What mineral is dark, greasy, and writes on paper?

Graphite.

Garnet

Mineral; silicate group; red-brown glassy crystals; often rounded/dodecahedral; no cleavage.

What mineral is usually red-brown, glassy, and forms rounded crystals?

Garnet.

Olivine

Mineral; silicate group; olive green; glassy/granular; common in mafic and ultramafic rocks.

What mineral is olive-green and common in mafic/ultramafic rocks?

Olivine.

Actinolite

Mineral; amphibole/silicate group; green; bladed, needle-like, or fibrous crystals.

What mineral is green and often needle-like, bladed, or fibrous?

Actinolite.

Muscovite

Mineral; mica/silicate group; light-colored mica; clear/silvery sheets; peels easily.

What mineral is light mica that peels into clear/silvery sheets?

Muscovite.

Kaolinite

Mineral; clay/silicate group; white or cream; earthy; soft, powdery, or crumbly.

What mineral is a soft white clay with an earthy texture?

Kaolinite.

Magnetite

Mineral; oxide group; black; metallic/submetallic; magnetic.

What mineral is black and magnetic?

Magnetite.

Basalt

Igneous rock; extrusive; mafic; dark-colored; fine-grained; may have tiny crystals or vesicles.

Dark, fine-grained, mafic extrusive igneous rock

Basalt.

Rhyolite

Igneous rock; extrusive; felsic; light-colored; fine-grained; volcanic equivalent of granite.

Light-colored, fine-grained, felsic extrusive igneous rock

Rhyolite.

Tuff

Igneous rock; extrusive/pyroclastic; made of volcanic ash; often light gray, crumbly, or fragmental.

Volcanic ash rock that may look crumbly or fragmental

Tuff.

Volcanic breccia

Igneous rock; extrusive/pyroclastic; angular volcanic fragments cemented together.

Igneous rock with angular volcanic fragments

Volcanic breccia.

Pumice

Igneous rock; extrusive; felsic; very vesicular/frothy; light-colored; very lightweight and may float.

Light-colored, frothy, very lightweight vesicular igneous rock

Pumice.

Gabbro

Igneous rock; intrusive; mafic; dark-colored; coarse-grained visible crystals.

Dark, coarse-grained, mafic intrusive igneous rock

Gabbro.

Obsidian

Igneous rock; extrusive; felsic/intermediate; black volcanic glass; smooth; conchoidal fracture.

Black glassy volcanic rock

Obsidian.

Granite

Igneous rock; intrusive; felsic; coarse-grained; light-colored; quartz, feldspar, and mica visible.

Light-colored, coarse-grained, felsic intrusive igneous rock

Granite.

Porphyritic andesite

Igneous rock; extrusive; intermediate; large crystals in fine-grained gray matrix.

Large crystals in a fine-grained gray intermediate volcanic matrix

Porphyritic andesite.

Vesicular basalt

Igneous rock; extrusive; mafic; dark fine-grained rock with gas-bubble holes.

Dark mafic volcanic rock with vesicles/gas-bubble holes

Vesicular basalt.

Scoria

Igneous rock; extrusive; mafic; dark red/black; vesicular; heavier and darker than pumice.

Dark red or black vesicular mafic volcanic rock

Scoria.

Diorite

Igneous rock; intrusive; intermediate; coarse-grained; black-and-white “salt and pepper” appearance.

Coarse-grained intermediate intrusive rock with salt-and-pepper appearance

Diorite.

Dunite / Peridotite

Igneous rock; intrusive; ultramafic; greenish/dark; olivine-rich; dense.

Greenish ultramafic intrusive rock rich in olivine

Dunite / Peridotite.

Sandstone

Sedimentary rock; clastic; sand-sized grains; gritty texture.

Clastic sedimentary rock with sand-sized grains

Sandstone.

Mudstone

Sedimentary rock; clastic; very fine-grained mud; dull/earthy; does not split into thin sheets as well as shale.

Very fine-grained clastic sedimentary rock made of mud

Mudstone.

Shale

Sedimentary rock; clastic; very fine-grained; splits into thin layers/fissile sheets.

Very fine-grained sedimentary rock that splits into thin layers

Shale.

Conglomerate

Sedimentary rock; clastic; rounded gravel-sized clasts cemented together.

Clastic sedimentary rock with rounded pebbles/clasts

Conglomerate.

Breccia

Sedimentary rock; clastic; angular gravel-sized clasts cemented together.

Clastic sedimentary rock with angular clasts

Breccia.

Fossiliferous limestone

Sedimentary rock; biochemical; visible fossils/shell fragments; reacts with acid.

Limestone with visible fossils or shell fragments

Fossiliferous limestone.

Micritic limestone

Sedimentary rock; chemical/biochemical; very fine-grained limestone; reacts with acid; smooth/dense.

Very fine-grained limestone that reacts with acid

Micritic limestone.

Oolitic limestone

Sedimentary rock; chemical/biochemical; small rounded ooids; reacts with acid.

Limestone made of small rounded ooids

Oolitic limestone.

Rock gypsum

Sedimentary rock; chemical; soft; white/clear/pinkish; made of gypsum; can be scratched by fingernail.

Soft chemical sedimentary rock made of gypsum

Rock gypsum.

Dolostone

Sedimentary rock; chemical/biochemical; made of dolomite; usually reacts weakly with acid unless powdered.

Sedimentary carbonate rock that reacts weakly with acid unless powdered

Dolostone.

Chert

Sedimentary rock; chemical/biochemical; hard microcrystalline quartz; waxy/glassy; conchoidal fracture.

Hard, waxy/glassy sedimentary rock with conchoidal fracture

Chert.

Slate

Metamorphic rock; foliated; low-grade; dull, very fine-grained; breaks into flat sheets/slaty cleavage.

Dull, fine-grained metamorphic rock that breaks into flat sheets

Slate.

Phyllite

Metamorphic rock; foliated; low-to-medium grade; satiny sheen; slightly wavy foliation; shinier than slate.

Foliated metamorphic rock with a satiny sheen

Phyllite.

Schist

Metamorphic rock; foliated; medium-to-high grade; visible mica flakes; sparkly; schistosity.

Sparkly foliated metamorphic rock with visible mica flakes

Schist.

Gneiss

Metamorphic rock; foliated; high-grade; distinct light and dark mineral banding.

High-grade metamorphic rock with light and dark banding

Gneiss.

Quartzite

Metamorphic rock; nonfoliated; metamorphosed sandstone; very hard; sugary quartz texture; breaks across grains.

Very hard nonfoliated metamorphic rock made of fused quartz grains

Quartzite.

Marble

Metamorphic rock; nonfoliated; metamorphosed limestone; crystalline/sugary calcite; reacts with acid.

Nonfoliated metamorphic rock made of crystalline calcite

Marble.