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Rocks and Minerals Cheat Sheet by

Minerals

Potassium Feldspar
H = 6
Salmon pink, white
Two cleavages at about 90 degrees
Plagioclase
H = 6
White to dark gray
Two cleavages at almost 90 degrees
Straight, parallel striations
Quartz
H = 7
Conchoidal fracture
Vitreous luster
Muscovite
H = 2-2.5
Colorless, silvery white, brownish silvery white
One perfect cleavage
Transparent, flexible, and elastic in thin sheets
Biotite
H = 2.5-3
Black to brownish black
One perfect cleavage
Flexible and elastic in thin sheets
Hornblende (Amphibole)
H = 5
Black
Two perfect cleavages at 124 and 56 degrees
Splintery
Augite (Pyroxene)
H = 5-6
Black to dark green
Two imperfect cleavages at almost 90 degrees
Olivine
H = 6.5-7
Olive green to yellow green
Granular
Gypsum
H = 2
Clear, white, light gray
Vitreous to pearly
Pyrite
H = 6-6.5
Metallic
Brass yellow
Calcite
H = 3
Clear, white, others
Three perfect cleavages form rhombic cleavage fragments
Reacts strongly with HCl
Dolomite
H = 3-3.5
Reacts slowly or not at all with HCl
Three indistinct cleavages
Halite
H = 2.5
Clear to gray to red
Three perfect cleavages at 90 degrees
Salty taste
 

Igneous Vocabulary

Phaneritic
Coarse­-gr­ained (>1 mm)
Aphanitic
Fine-g­rained (<1 mm)
Pegmatitic
Except­ionally large crystals (>3 cm)
Porphy­ritic
Two crystal sizes
Phenoc­rysts
Larger crystals
Groundmass
Smaller crystals surrou­nding phenoc­rysts
Vesicular
Bubbles
Pyrocl­astic
Multiple fragments

Igneous Rocks

Gabbro (phane­ritic)
Intrusive, mafic
Ca-plagioclase, black pyroxene, olivine
Diorite (phane­ritic)
Intrusive, intermediate
Na-Ca-plagioclase and hornblende
Biotite and quartz
Granite (phane­ritic)
Intrusive, felsic
Quartz and K-feldspar
Na-plagioclase, biotite, and hornblende
Granite (porph­yritic)
Intrusive, felsic
Coarse-grained
Two crystal sizes
Granite pegmatite
Intrusive, felsic
Very coarse­-gr­ained
Basalt (aphan­itic)
Extrusive, mafic
Dark gray
Ca-plagioclase and olivine
Basalt (vesic­ular)
Extrusive, mafic
Dark gray
Ca-plagioclase and olivine
Andesite (porph­yritic)
Extrusive, intermediate
Fine-grained
Gray
Plagioclase and hornblende or biotite
Rhyolite
Extrusive, felsic
Fine-grained version of granite
Tuff (pyroc­lastic)
Extrusive
Particle size less than 6.4 cm
Obsidian (glassy)
Extrusive, felsic
Pumice
Extrusive, felsic
Vesicular
Very light
Scoria
Extrusive, mafic
Vesicular
Black to reddish brown

Metamo­rphic Vocabulary

Foliated
Parallel or nearly parallel planes
Slaty
Foliation made of minerals to small to see without a microscope
Phyllitic
Foliation composed of minerals visible with handlens to barely visible to naked eye
Schistose
Foliation composed of mineral crystals large enough to see unaided
Gneissic
Coarse foliation
Parallel band or layers of light and dark minerals

Metamo­rphic Rocks

Foliated
Slate
Low grade; Very fine grained
Generally dark
Shale or mudstone
Phyllite
Low grade; Fine grained
Silky, shiny
Shale or mudstone
Schist
Intermediate
Medium to coarse grained
Shale or mudstone
Gneiss
High grade
Medium to coarse grained
Shale, mudstone, or granite
Migmatite
Border between igneous and metamorphic
Medium to coarse grained
Shale, mudstone, or granite
Nonfoliated
Marble
Grade varies
Coarsely crystalline
Limestone or dolostone
Quarzite
Grade varies
Crystalline
Quartz sandstone
Anthracite coal
Low to medium grade
Conchoidal fracture
Coal
Greenstone
Low to medium grade
Greenish gray to black
Basalt or gabbro
Amphib­olite
Medium to high grade
Dark gray to black
Medium to coarse grained
Basalt or gabbro
Soapstone
Low to medium grade
Gray to dark greenish gray
Fine grained; Soft
Peridotite
Serpen­tinite
Variable grade
Greenish
Mottled or streaked
Peridotite
Metaconglomerate
Low to medium grade
Conglomerate, graywacke, chert
Hornfels
Low grade; Contact
Fine grained; Dark
Varies
 

Sedime­ntary Rocks

Quartz sandstone
Sand grains of quartz
White, rusty brown
Conglo­merate
Made of pebbles
Limestone
Calcite
Bubbles in acid
Shale
Fissile
Black to gray, red, or green
Dolostone
Lesser reaction with acid
Crystalline
Light gray or buff
Chert
Microc­rys­talline quartz
Conchoidal fracture
Coal
Brown to black
Noncrystalline
Mudstone
Not fissile
Black to gray, red, or green
Sandstone
Made of sand
Oolite
Limestone
Sand-sized spheres
Coquina
Limestone
Poorly cemented bioclastic debris
Breccia
Angular particles
Rock Gypsum
White, light gray
Crystalline

Sedime­ntary Vocabulary

Clastic
Clasts bound together
Bioclastic
Abundant fossils or fossil fragments
Crystalline
Interl­ocking crystals
Fissile
Splits into sheets
                       
 

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