Mineralogy Exam 1

Unknown Hand Samples

• Hardness: 3

• Luster: Vitreous

• Color/Streak: Colorless; white streak

• Cleavage: Perfect rhombohedral

• Special: Effervesces with HCl

calcite

• Hardness: 3.5–4

• Luster: Vitreous

• Color/Streak: Pink; white streak

• Cleavage: Perfect rhombohedral

• Special: Reacts with HCl when powdered

Rhodochrosite

• Hardness: 3.5–4

• Luster: Vitreous

• Color/Streak: White or colorless

• Cleavage: Poor

• Special: Orthorhombic form of CaCO₃

Aragonite

• Hardness: 3.5–4.5

• Luster: Vitreous to dull

• Color/Streak: White; white streak

• Cleavage: Rhombohedral

• Special: Reacts slowly with HCl when powdered

Magnesite

• Hardness: 5–5.5

• Luster: Adamantine to dull

• Color/Streak: Brown; yellow-brown streak

• Cleavage: None

• Special: Brown earthy masses

goethite

• Hardness: 5–6.5

• Luster: Metallic to earthy

• Color/Streak: Red-brown streak

• Cleavage: None

• Special: High density, weak magnetism

Hematite

• Hardness: 5.5–6.5

• Luster: Metallic

• Color/Streak: Black; black streak

• Cleavage: None (subconchoidal fracture)

• Special: Strongly magnetic

Magnetite

• Hardness: 5.5–6

• Luster: Vitreous to greasy

• Color/Streak: Gray, greenish, colorless; white streak

• Cleavage: Poor

• Special: Gelatinizes with HCl; no quartz present in host rock

nephaline

• Hardness: 6–6.5

• Luster: Vitreous

• Color/Streak: White to gray; white streak

• Cleavage: Perfect in two directions at ~90°

• Special: Plagioclase feldspar end member

Albite

• Hardness: 6–6.5

• Luster: Vitreous

• Color/Streak: Gray to dark; white streak

• Cleavage: Perfect in two directions at ~90°

• Special: Distinctive labradorescence (iridescent play of colors)

Labradorite

• Hardness: 5–5.5

• Luster: Vitreous

• Color/Streak: Colorless to white; white streak

• Cleavage: Poor to indistinct

• Special: Zeolite group; trapezohedral crystals

Anaclime

• Hardness: ~5.5–6 (matrix varies)

• Luster: Dull to vitreous

• Color/Streak: Gray, greenish; white streak

• Cleavage: Poor (feldspar shows good cleavage)

• Special: Quartz-free feldspathoid rock

Nephalite Syenite

• Hardness: 6–6.5

• Luster: Vitreous

• Color/Streak: White to gray; white streak

• Cleavage: Perfect in two directions at ~90°

• Special: Plagioclase feldspar (Ca-rich)

Bytownite

• Hardness: 6–6.5

• Luster: Vitreous

• Color/Streak: White to grayish; white streak

• Cleavage: Perfect in two directions at ~90°

• Special: Plagioclase feldspar (Na-rich)

Oligoclase

• Hardness: 6–6.5

• Luster: Vitreous

• Color/Streak: White to gray; white streak

• Cleavage: Perfect in two directions at ~90°

• Special: Common striations on cleavage faces

Plagioclase

• Hardness: 6

• Luster: Vitreous

• Color/Streak: Pink, white, colorless; white streak

• Cleavage: Perfect in two directions at ~90°

• Special: K-feldspar end member

Orthoclase

• Hardness: 6

• Luster: Vitreous

• Color/Streak: Pink, white, colorless; white streak

• Cleavage: Perfect in two directions at ~90°

• Special: K-feldspar end member

Orthoclase

• Hardness: 5.5–6

• Luster: Vitreous to greasy

• Color/Streak: Blue, gray; white streak

• Cleavage: Poor

• Special: Feldspathoid group; may fluoresce orange

Sodalite

• Hardness: 6

• Luster: Vitreous

• Color/Streak: Pink to flesh-colored; white streak

• Cleavage: Perfect in two directions at ~90°

• Special: Intergrowth of K-feldspar and albite (visible lamellae)

Perthite

• Hardness: 6

• Luster: Vitreous

• Color/Streak: Pink, white, colorless; white streak

• Cleavage: Perfect in two directions at ~90°

• Special: K-feldspar end member

Orthoclase

• Hardness: 5.5–6

• Luster: Vitreous to dull

• Color/Streak: White, gray; white streak

• Cleavage: Poor to none

• Special: Feldspathoid group; typically forms icositetrahedral crystals

Leucite

• Hardness: 6

• Luster: Vitreous

• Color/Streak: Pink to flesh-colored; white streak

• Cleavage: Perfect in two directions at ~90°

• Special: Intergrowth of K-feldspar and albite (visible lamellae)

Perthite

• Hardness: 6–6.5

• Luster: Vitreous

• Color/Streak: White, pink, green; white streak

• Cleavage: Perfect in two directions at ~90°

• Special: Cross-hatched (grid) twinning diagnostic

microcline

• Hardness: 6–6.5

• Luster: Vitreous

• Color/Streak: Green to blue-green; white streak

• Cleavage: Perfect in two directions at ~90°

• Special: Microcline variety with distinctive color

Amazonite

• Hardness: 5–6.5

• Luster: Vitreous to waxy

• Color/Streak: Varied; white streak

• Cleavage: None (conchoidal fracture)

• Special: Fossilized wood replaced by opal

Opalized Wood

• Hardness: 6.5–7

• Luster: Waxy to vitreous

• Color/Streak: Banded multicolored; white streak

• Cleavage: None (conchoidal fracture)

• Special: Banded chalcedony (cryptocrystalline quartz)

Agate

• Hardness: 3–4.5

• Luster: Metallic

• Color/Streak: Steel-gray to black; dark gray streak

• Cleavage: Indistinct

• Special: Copper antimony sulfide; tetrahedral crystals

Tetrahedrite

• Hardness: 6.5–7

• Luster: Waxy

• Color/Streak: White to bluish; white streak

• Cleavage: None (conchoidal fracture)

• Special: Cryptocrystalline quartz variety

Chalcedony

• Hardness: 6.5–7

• Luster: Dull to waxy

• Color/Streak: Varied (gray, brown); white streak

• Cleavage: None (conchoidal fracture)

• Special: Dense, microcrystalline quartz

Chert

• Hardness: ~5–6

• Luster: Glassy

• Color/Streak: Black to dark brown; no streak (or gray)

• Cleavage: None (conchoidal fracture)

• Special: Natural volcanic glass

Obsidian

• Color: Gray, brown, tan with angular fragments.

• Luster: Dull to waxy.

• Hardness: ~7 (like quartz).

• Fracture: Conchoidal on chert pieces; jagged at breccia boundaries.

• Diagnostic: Mixture of angular chert fragments cemented together — looks like a “broken mosaic.”

Chert Breccia

• Color: Brown to black smoky tint.

• Luster: Vitreous (glassy).

• Hardness: 7.

• Cleavage: None; conchoidal fracture.

• Diagnostic: Transparent to translucent quartz with smoky coloration due to natural radiation.

Smoky Quartz

• Color: Purple to violet.

• Luster: Vitreous.

• Hardness: 7.

• Cleavage: None; conchoidal fracture.

• Diagnostic: Purple quartz variety — color is key.

Amethyst

• Color: White to cloudy white.

• Luster: Vitreous to dull.

• Hardness: 7.

• Cleavage: None; conchoidal fracture.

• Diagnostic: Cloudy white quartz variety — looks “milky.”

Milky Quartz

• Color: Gray, brown, black, red.

• Luster: Dull to waxy.

• Hardness: 7.

• Fracture: Conchoidal.

• Diagnostic: Microcrystalline quartz — very hard, breaks like glass.

Chert

• Color: Banded — many colors.

• Luster: Waxy to vitreous.

• Hardness: 7.

• Cleavage: None.

• Diagnostic: Banded chalcedony (microcrystalline quartz) — concentric or wavy stripes.

Agate

• Color: Brown to black smoky tint.

• Luster: Vitreous (glassy).

• Hardness: 7.

• Cleavage: None; conchoidal fracture.

• Diagnostic: Transparent to translucent quartz with smoky coloration due to natural radiation.

Smoky Quartz

• Color: Pink to rose-red.

• Luster: Vitreous.

• Hardness: 7.

• Cleavage: None; conchoidal fracture.

• Diagnostic: Pink quartz variety — usually massive, not crystals.

Rose Quartz

• Color: Dark gray to black.

• Luster: Dull to waxy.

• Hardness: 7.

• Fracture: Conchoidal.

• Diagnostic: Dark, fine-grained chert used historically for tools and fire-starting.

Flint

• Color: Brown, tan, sometimes rainbow/iridescent.

• Luster: Vitreous.

• Hardness: ~5.5–6.5.

• Cleavage: None.

• Diagnostic: Petrified wood replaced by opal — retains wood structure but with opal’s appearance.

Opalized Wood

• Color: Brown, tan, or multi-colored with possible iridescence.

• Luster: Vitreous to waxy.

• Hardness: ~5.5–6.5.

• Cleavage: None.

• Diagnostic: Fossil wood replaced by opal (hydrated silica); keeps tree-ring texture but has opal’s look.

Opal Petrified Wood

• Color: Gray, brown, black, red.

• Luster: Dull to waxy.

• Hardness: 7.

• Fracture: Conchoidal.

• Diagnostic: Microcrystalline quartz — very hard, breaks like glass.

Chert

• Color: Outer rind gray/brown, interior lined with quartz or calcite crystals of various colors.

• Luster: Dull outside, vitreous inside.

• Hardness: Depends on inner mineral (quartz ~7).

• Cleavage: None.

• Diagnostic: Hollow nodule with a crystalline interior — you see a “crust with sparkles inside.”

Geode

• Color: Yellow to orange quartz.

• Luster: Vitreous.

• Hardness: 7.

• Cleavage: None; conchoidal fracture.

• Diagnostic: Transparent yellow quartz variety — color from iron.

Citrine

• Color: Red, brown, yellow, green; opaque.

• Luster: Dull to waxy.

• Hardness: 7.

• Cleavage: None; conchoidal fracture.

• Diagnostic: Opaque, fine-grained chalcedony; uniform color or mottled

Jasper

• Color: Pale brass-yellow, tarnishes dark.

• Luster: Metallic.

• Hardness: 6–6.5.

• Cleavage: Good on {010}.

• Diagnostic: Often tabular or cockscomb aggregates; lighter and more brittle than pyrite.

Marcasite

• Color: Bronze to brownish-bronze.

• Luster: Metallic.

• Hardness: 3.5–4.5.

• Cleavage: Poor.

• Diagnostic: Magnetic (weak to strong); bronze color; streak gray-black.

Pyrrhotite

• Color: Steel-gray to silver-white.

• Luster: Metallic.

• Hardness: 5.5–6.

• Cleavage: Distinct {010}.

• Diagnostic: Garlic odor when struck or heated; wedge-shaped crystals.

Arsenopyrite

• Color: Lead-gray with bluish tint.

• Luster: Metallic.

• Hardness: 1–1.5.

• Cleavage: Perfect basal {0001}.

• Diagnostic: Greasy feel; marks paper; resembles graphite but with bluish tinge.

Molybdendite

• Color: Lead-gray to steel-gray.

• Luster: Metallic.

• Hardness: 2.

• Cleavage: Perfect {010}.

• Diagnostic: Elongate prismatic crystals with striations; soft and dense antimony sulfide.

Stibnite

• Color: Bright lemon-yellow to orange-yellow.

• Luster: Resinous to pearly.

• Hardness: 1.5–2.

• Cleavage: Perfect {010}.

• Diagnostic: Soft, sectile, yellow arsenic sulfide with a garlic odor when heated.

Orpiment

• Color: Silvery-white metallic.

• Luster: Metallic.

• Hardness: 2.5–3.

• Cleavage: None.

• Diagnostic: Malleable native metal; bright metallic silver color; high density.

Silver

• Color: Steel-gray to black.

• Luster: Metallic to dull.

• Hardness: 1–2.

• Cleavage: Perfect basal {0001}.

• Diagnostic: Marks paper easily; greasy feel; low specific gravity compared to metallic look.

Graphite

• Color: Golden yellow.

• Luster: Metallic.

• Hardness: 2.5–3.

• Cleavage: None.

• Diagnostic: Malleable native metal; yellow streak; high density.

Gold

• Color: Bright yellow.

• Luster: Resinous to greasy.

• Hardness: 1.5–2.5.

• Cleavage: Poor.

• Diagnostic: Light, low-density crystals; burns with blue flame and smell of SO₂.

Sulfur

• Color: Lead-gray.

• Luster: Metallic.

• Hardness: 2.5–3.

• Cleavage: Perfect cubic {100}.

• Diagnostic: Very heavy lead ore; cubic crystals; gray-black streak.

Galena

• Color: Scarlet red.

• Luster: Adamantine to dull.

• Hardness: 2–2.5.

• Cleavage: Perfect {101̅0}.

• Diagnostic: Red mercury sulfide; dense; vermilion streak.

Cinnabar

• Color: Dark gray to black with metallic luster.

• Luster: Metallic.

• Hardness: 2.5–3.

• Cleavage: Poor.

• Diagnostic: Copper sulfide; very heavy; sooty-black streak.

Chalcocite

• Color: Brown, yellow, black.

• Luster: Resinous to submetallic.

• Hardness: 3.5–4.

• Cleavage: Perfect dodecahedral {110}.

• Diagnostic: Pale yellow streak with sulfur smell; main zinc ore.

Sphalerite

• Color: Brass-yellow, often iridescent tarnish.

• Luster: Metallic.

• Hardness: 3.5–4.

• Cleavage: Poor.

• Diagnostic: Common copper iron sulfide; softer than pyrite; green-black streak.

Chalcopyrite

• Color: Gray, brown, red (ruby), blue (sapphire).

• Luster: Vitreous to adamantine.

• Hardness: 9 (second only to diamond).

• Cleavage: None; parting on {0001}.

• Diagnostic: Extremely hard; hexagonal barrel-shaped crystals.

Corundum

• Color: Brownish-black to black.

• Luster: Metallic to submetallic.

• Hardness: 5.5.

• Cleavage: Poor.

• Diagnostic: Heavy black ore of chromium; brown streak.

Chromite

• Color: Reddish-brown, black, or golden-yellow.

• Luster: Adamantine to metallic.

• Hardness: 6–6.5.

• Cleavage: Distinct on {110}.

• Streak: Light brown.

• Diagnostic: High luster and reddish-brown color; slender prismatic or needle-like crystals; very high density; often found as inclusions in quartz (producing “rutilated quartz”).

Rutile

• Color: Brown to black.

• Luster: Adamantine to submetallic.

• Hardness: 6–7.

• Cleavage: None, but has distinct parting.

• Diagnostic: Heavy tin oxide; high luster; brown streak.

Cassiterite

• Color: Wide range — purple, green, blue, yellow, colorless.

• Luster: Vitreous (glassy).

• Hardness: 4 (index mineral on Mohs scale).

• Cleavage: Perfect in four directions, forming octahedra.

• Streak: White.

• Diagnostic: Transparent to translucent crystals; octahedral cleavage is very distinctive; may fluoresce under UV light.

Fluorite

• Color: Yellow, reddish-brown.

• Luster: Resinous.

• Hardness: 5–5.5.

• Cleavage: Poor.

• Diagnostic: Heavy rare-earth phosphate; typically granular in sands.

Monazite

• Color: Green, blue, brown, colorless.

• Luster: Vitreous to subresinous.

• Hardness: 5 (index for Mohs scale).

• Cleavage: Poor {0001}.

• Diagnostic: Hexagonal crystals; scratched easily by knife but not fingernail.

Apatite

Color: Colorless to white, sometimes reddish.

• Luster: Vitreous.

• Hardness: 2.

• Cleavage: Perfect cubic {100}.

• Diagnostic: Tastes bitter (KCl); softer and lighter than halite.

Sylvite

• Color: Brown, yellow-brown, gray.

• Luster: Vitreous to pearly.

• Hardness: 3.5–4.5.

• Cleavage: Perfect rhombohedral {101̅1}.

• Diagnostic: Iron carbonate; effervesces slowly in warm HCl.

Siderite

• Color: Colorless to white, can be pink, gray, etc.

• Luster: Vitreous.

• Hardness: 2.5.

• Cleavage: Perfect cubic {100}.

• Diagnostic: Salty taste; dissolves in water; clear to translucent cubes.

Halite

• Color: Bright green, banded.

• Luster: Silky to earthy.

• Hardness: 3.5–4.

• Cleavage: Perfect in one direction (rare).

• Diagnostic: Green copper carbonate with botryoidal masses; effervesces in acid.

Malachite

• Color: Brown to black.

• Luster: Adamantine to submetallic.

• Hardness: 6–7.

• Cleavage: None, but has distinct parting.

• Diagnostic: Heavy tin oxide; high luster; brown streak.

Cassiterite

• Color: Colorless, white, gray.

• Luster: Vitreous to silky.

• Hardness: 2 (can be scratched by fingernail).

• Cleavage: Perfect {010}.

• Diagnostic: Very soft calcium sulfate; forms clear selenite or fibrous satin spar.

Gypsum

• Color: Colorless, white, gray, blue, lilac.

• Luster: Vitreous to pearly.

• Hardness: 3–3.5.

• Cleavage: Perfect {010}, {100}, {001} (three directions at right angles).

• Diagnostic: Looks like gypsum but harder and does not effervesce; lacks water in its structure.

Anhydrite

• Color: Colorless, white, yellow, blue.

• Luster: Vitreous to pearly.

• Hardness: 3–3.5.

• Cleavage: Perfect {210}.

• Diagnostic: Very heavy for a nonmetallic mineral (BaSO₄); tabular crystals.

Barite

• Color: Colorless to pale blue or gray.

• Luster: Vitreous to pearly.

• Hardness: 3–3.5.

• Cleavage: Perfect {001}.

• Diagnostic: Strontium sulfate; heavier than gypsum; pale sky-blue crystals common.

celestite

• Color: White, gray, bluish or greenish.

• Luster: Pearly to vitreous.

• Hardness: 2.5.

• Cleavage: Perfect {0001}.

• Diagnostic: Soft Mg hydroxide; flakes easily; feels slippery.

Brucite

• Color: White, gray, brown, reddish.

• Luster: Dull to earthy.

• Hardness: 1–3.

• Cleavage: None.

• Diagnostic: Aluminum ore with pea-sized pisolites (tiny round grains); very low density.

Bauxite

• Color: Brown, yellow-brown, gray.

• Luster: Vitreous to pearly.

• Hardness: 3.5–4.5.

• Cleavage: Perfect rhombohedral {101̅1}.

• Diagnostic: Iron carbonate; effervesces slowly in warm HCl.

Siderite

• Color: Colorless, white, grayish.

• Luster: Vitreous to resinous.

• Hardness: 3–3.5.

• Cleavage: Distinct {010}.

• Diagnostic: Barium carbonate; heavy; reacts with acid to release CO₂.

Witherite

• Color: Colorless, gray, white.

• Luster: Adamantine.

• Hardness: 3–3.5.

• Cleavage: Distinct {110}.

• Diagnostic: Heavy lead carbonate; high luster and density; twinned crystals common.

Cerussite

• Color: Green, blue, pink, brown, gray.

• Luster: Vitreous to pearly.

• Hardness: 4–5.

• Cleavage: Perfect rhombohedral {101̅1}.

• Diagnostic: Zinc carbonate; botryoidal masses; effervesces in acid.

Smithsonite

• Color: Deep blue.

• Luster: Vitreous.

• Hardness: 3.5–4.

• Cleavage: Perfect in one direction (rare).

• Diagnostic: Blue copper carbonate; effervesces in acid; often with malachite.

Azurite

• Color: Colorless, white, yellowish, greenish.

• Luster: Vitreous.

• Hardness: 3.5–4.

• Cleavage: Perfect {110}.

• Diagnostic: Strontium carbonate; radiating fibrous crystals.

Strontianite

• Color: Colorless, white, gray, pink.

• Luster: Vitreous to pearly.

• Hardness: 3.5–4.

• Cleavage: Perfect rhombohedral {101̅1}.

• Diagnostic: Effervesces weakly in cold acid but strongly when powdered; curved crystal faces common.

Dolomite