Geology 1403 Rock and Mineral Practical

Which rocks have porphyritic textures?

Andesite

Which kind of rock is likely to form at a divergent boundary?

Basalt

Which rocks have fine-grained textures?

Basalt, dunite

Fossiliferous Limestone

Biochemical Composition: Calcite Fossilized shell in a fine-grained matrix

Chalk

Biochemical Composition: Calcite Microscopic shells Powdery

Oolitic Limestone

Biochemical Composition: Calcite Spherical grains (Ooids)

Bituminous Coal

Chemical Organic Composition: Carbonized plant fragments Black to dark brown Brittle Sooty

Peat

Chemical Organic Composition: Plant fragments Visible plant fragments

Garnet

Color varies with composition, silicate, usually red-brown, uneven fracture, resinous (or vitreous), Conchoidal fracture and parting, abrasives, gemstones, H:6.5-7.5

Calcite

Colorless to white, yellow, pink, blue/gray, or brown, fizzes in HCl, 3 directions of cleavage NOT at 90 degrees (rhombohedral) glassy luster, double refraction, H=3, CaCO3

Copper

Copper color, metallic luster, tarnishes brown or green, copper colored streaks, forms odd shaped masses, no cleavage, H=2.5-3

Are rocks likely to be darker or lighter than those at the bottom of Bowen's Reaction Series?

Darker on top

Arkose

Detrital Abundant Feldspar (>15%) Rock fragments and mineral grains Gravel size (>2mm)

Breccia

Detrital Angular rock fragments and mineral grains Gravel size (>2mm)

Shale

Detrital Mostly clay minerals Clay size (<1/256mm)

Lithic Sandstone

Detrital Mostly rock fragments Sand size (1/16mm-2mm)

Quartz Sandstone

Detrital Mostly rounded quartz grains Sand size (1/16mm-2mm)

Conglomerate

Detrital Rounded rock fragments and mineral grains Gravel size (>2mm)

Pumice

F,I,M,UM: Felsic Texture: Vesicular Mineral composition: silica content, iron, magnesium Other properties: extremely lightweight; long (horizontal) holes in the rock Inferred rock origin: extrusive lava flow; usually a rhyolitic explosion

Tuff

F,I,M,UM: Felsic Texture: coarse-grained Mineral composition: pyroclastic rocks Other properties: Consists of large rocks and small rocks. It has a white/gray/black color. Inferred rock origin: Intrusive

Granite

F,I,M,UM: Felsic Texture: coarse-grained Mineral composition: quartz, orthoclase feldspar, biotite, hornblende Other properties: combinations of pink, black, white; large crystals Inferred rock origin: Intrusive; single cooling; pyroclastic deposit. The coarse-grained version of rhyolite.

Rhyolite

F,I,M,UM: Felsic Texture: fine-grained or porphyritic Mineral composition: lava rock of orthoclase feldspar and quartz Other properties: pink to gray color; crystals may be all the same size (small) or a combination of large and small Inferred rock origin: Extrusive; nonviolent volcanic eruption. The fine-grained version of granite.

Obsidian

F,I,M,UM: Felsic/Intermediate Texture: glassy/no grains/fine-grained Mineral composition: silicon dioxide Other properties: extremely smooth texture, typically black color, and glassy appearance Inferred rock origin: extrusive lava flow

Syenite

F,I,M,UM: Intermediate Texture: Coarse-grained Mineral composition: alkalic feldspar, hornblende/biotite Other properties: different-colored rock combinations. May be pink, white, black, gray Inferred rock origin: Intrusive

Andesite

F,I,M,UM: Intermediate Texture: Porphyritic Mineral composition: andesine and one or more mafic constituents Other properties: large and small crystals. Color can be gray with white to light gray phenocrysts. Inferred rock origin: Extrusive; violent volcanic eruption. The fine-grained version (?) of diorite.

Diorite

F,I,M,UM: Intermediate Texture: coarse-grained Mineral composition: sodic plagioclase, hornblende, biotite, or pyroxene Other properties: similar in appearance to granite - black and white combinations Inferred rock origin: intrusive. The coarse-grained version of andesite.

Scoria

F,I,M,UM: Mafic Texture: Vesicular Mineral composition: basalt Other properties: Has many holes in it; lightweight; reddish color Inferred rock origin: extrusive lava flow; a basaltic (very explosive) volcanic explosion

Gabbro

F,I,M,UM: Mafic Texture: coarse-grained Mineral composition: feldspar and pyroxene Other properties: dark colored typically. Larger crystals than basalt. Inferred rock origin: Intrusive. The coarse-grained version of basalt.

Basalt

F,I,M,UM: Mafic Texture: fine-grained Mineral composition: plagioclase feldspar, augite, olivine Other properties: dark appearance. Small crystals. Inferred rock origin: Extrusive. Very violent volcanic eruption. The fine-grained version of gabbro.

Peridotite

F,I,M,UM: Ultra-mafic Texture: Coarse-grained Mineral composition: olivine, pyroxene Other properties: dark green to black color. Inferred rock origin: Intrusive. The coarse-grained version of komatiite.

Dunite

F,I,M,UM: Ultra-mafic Texture: fine-grained Mineral composition: pyroxene, plagioclase, olivine Other properties: yellow/green color due to olivine content Inferred rock origin: intrusive. Essentially it's peridotite but it consists of a lot of olivine.

Granitic Gneiss

Foliated Coarse grained Alternating light and dark mineral bands

Schist

Foliated Coarse grained Visible crystals of platy minerals Breaks along scaly foliated surfaces Many mineral varieties; Mica, garnet, chlorite....

Slate

Foliated Dull luster Very fine-grained Breaks into hard, flat sheets (Slaty rock cleavage) Rings when tapped with a nail

Phyllite

Foliated Satiny sheen Fine-grained Breaks along wrinkled or wavy foliated surfaces Small micaceous minerals are barely visible

Rock Gypsum

Inorganic Composition: Gypsum Softer than your fingernail Sugary appearance

Rock Salt

Inorganic Composition: Halite Crystalline structure Salty taste Softer than glass

Chert

Inorganic Composition: Quartz Microcrystalline, often waxy appearance Conchoidal fracture Harder than glass

Would you expect to find olivine and quartz in the same rock?

No, because quartz and olivine form at very different temperatures

Bauxite

Non-metallic luster, variable hardness, variable colors, pea-shaped clasts called pisolites, aluminum ore,

Serpentinite

Nonfoliated Coarse and fine-grained Dark with dull luster Contains the mineral serpentine (greenish, bladed crystals with glossy or waxy luster)

Marble

Nonfoliated Coarse grained Calcite crystals fused together Many color varieties Reacts with acid Softer than glass

Quartzite

Nonfoliated Coarse grained Quartz sand grains fused together Grains will not rub off like sandstone Harder than glass

Anthracite Coal

Nonfoliated Fine grained Black Shiny luster Composed of carbon

Hornfels

Nonfoliated Fine-grained Dark gray, green or black Microcrystalline Mostly small crystals, but may contain larger crystals of specific minerals)

Which rocks have glassy textures?

Obsidian

Olivine

Olive green, light to dark green, small granular grains, single crystals rare, sugary aggregates, vitreous luster, conchoidal and uneven fracture, H=6.5-7, refractories, (MgFe)2SiO4

Hematite ( earthy)

Red to reddish brown, dull luster, no cleavage, red streaks, H=1.5

Which rocks have pyroclastic textures?

Rhyolite, tuff

Which kinds of rock are likely to form at a convergent boundary?

Rhyolite/granite, andesite/diorite

Which rocks have vesicular textures?

Scoria, pumice

Which rocks have coarse-grained textures?

Tuff, granite, gabbro, syenite, diorite

Magnetite

black to dark gray, magnetic, metallic luster, crystalline masses, uneven fracture, black streak, octahedral, H=6, iron ore, Fe2O4

Sulfur

bright yellow, powdery masses, dull/earthy luster, rotten egg smell, H=1.5-2.5

3: Muscovite

colorless to light tan, perfect cleavage in one direction (basal/sheet) transparent in thin sheets, electrical insulators, fireproofing material, glassy luster, elastic, H=2-3

Biotite

dark brown to black,flexible, mica, one perfect cleavage, H:2-3

Pyroxene

dark green to black, two directions of cleavage at 90 degrees, dull luster, H=5.5-6, augite

Amphibole

dark green to black,prismatic cleavage, two directions of cleavage in 2 directions at 60 or 120 degrees, bright reflections off cleavage surface, long slender crystals, splintery fracture, glassy luster, H=5-6, Asbestos, (Hornblende)

Serpentine

dark to light green, greasy to waxy luster, H:3-5

Sphalerite

dark, crystalline masses, metallic luster on crystal face, resinous luster on cleavage surfaces, yellow streak, rotten egg odor when scratched, H=3.5-4, ZnS

Pyrite

gold, crystalline masses or cubic crystal form, no cleavage, metallic luster, "fools gold", black streak, striated faces, H=6-6.5 Pale brass color, FeS2

Graphite

gray, polymorph, metallic luster,H:1-2, 6 sided foliated masses, dry lubricant, pencil lead, made of Carbon, crystal sheets

Porphyritic Phaneritic

lager crystals surrounded by smaller crystals, two stages of cooling, booth slow, matrix

Quartz

many color variations, occurs as crystallized masses or 6 sided single crystal forms (hexagonal pyramids and prisms) glassy luster, conchoidal fracture, H=7, SiO2

Dolomite

non-metallic luster, rhombohedral cleavage, will fizz with HCl when powdered, H:3.5, Cement, CaMg(CO3)2

Aphanitic

non-visible(difficult to distinguish minerals), very fine-grained, rapid cooling rate, volcanic

Porphyritic aphanitic

phenocrysts in an aphanitic groundmass, two stages of cooling, first slow, second rapid

Gypsm

pink to white, dull, non-metallic luster, cleavage in one direction-poor in two others, satiny luster, tranparent, H=2, CaSO4

Fluorite

purple or green or clear color, translucent or transparent, cubic crystals, 4 directions of cleavage (octahedral), glassy luster, H=4, Vitreous, Flourine Gas, CaF2

Galena

silver gray color, metallic luster, cubic cleavage,gray streak, lead ore, H:2.5, High specific gravity, PbS

Hematite (specular)

silver to steel gray, metallic luster (glitter like flakes) uneven fracture, may have red-brown streaks, H=5-6, Iron ore, Fe2O3

Halite

usually colorless to white, cleavage in 3 directions at 90 degrees (cubic), salty taste, glassy luster, H=2.5, NaCl

Corundum

various colors, dull luster to vitreous, blue (sapphire) or red (ruby), no cleavage, barrel-shaped 6 sided crystal, H=9, Al2O3

Phaneritic

visible (individual minerals can be determined), coarse- grained, slow cooling rate, plutonic

Potassium Feldspar

white or orange pink, Felsic, Silicate, two directions of cleavage at 90 degrees, porcelain, glassy luster, H=6, KAlSi3O8

Talc

white or pale green, pearly luster, feels soapy or greasy, H=1, Ceramics, talcum powder

Plagioclase Feldspar

white to dark gray, two directions of cleavage at 90 degrees, Silicate, striations common, usually on one cleavage face, glassy luster, H=6, Ceramics, can be Sodium or Calcium feldspar

Kaolinite

white, dull luster, occurs in powdery masses, earthy smell, H=2-2.5, ceramic and porcelain

Limonite

yellow to dark brown, dull luster, rusty smell, yellowish brown streak, iron ore H=5-5.5, Fe2O3