Page 105 - Laboratory Manual in Physical Geology

METALLIC AND SUBMETALLIC (M) MINERAL IDENTIFICATION

STEP 1: STEP 2: STEP 3: STEP 4: STEP 5:
What is the Does the What is the Match the mineral’s Mineral name. Find
mineral’s mineral mineral’s physical properties to other out more about it in
hardness? have streak? characteristic properties the mineral
cleavage? below. database (Fig.3.21).

Color silvery gold; Tarnishes brown; H 6–6.5; Brittle;
HARD conchoidal to uneven fracture; Crystals: cubes (may be
(H > 5.5) striated), pyritohedrons, or octahedrons; Distinguished Pyrite
Scratches glass Dark gray from chalcopyrite, which is soft
to black
Not scratched Silvery dark gray to black; Tarnishes gray or rusty
by masonry nail yellow-brown; Strongly attracted to a magnet and may Magnetite
or knife blade be magnetized; H 6–6.5; Crystals: octahedrons
Cleavage Color submetallic silvery brown; Tarnishes to dull and
absent, Yellow-brown earthy yellow-brown to brown rust colors; H 1–5.5; Limonite
poor, or More commonly occurs in its nonmetallic yellow to
not visible brown forms (H 1–5)
HARD Color silvery black to black; Tarnishes gray to black;
or Brown H 5.5–6; May be weakly attracted to a magnet; Chromite
SOFT Crystals: octahedrons
Color steel gray, reddish-silver, to glittery bright silver
Red to (var. specular); Both metallic varieties have the Hematite
red-brown characteristic red-brown streak; May be attracted to a
magnet; H 5–6; Also occurs in nonmetallic, dull to
earthy, red to red-brown forms
Color bright silvery gray; Tarnishes dull gray; Brittle:
Dark gray breaks into cubes and shapes made of cubes; H 2.5; Galena
to black Crystals: cubes or octahedrons; Feels heavy for its
Cleavage size because of high specific gravity
good to
excellent Color silvery yellow-brown, silvery red, or black with
White to pale submetallic to resinous luster; Tarnishes brown or Sphalerite
yellow-brown black; H 3.5–4.0; smells like rotten eggs when
scratched, powdered, or in acid test
Color bright silvery gold; Tarnishes bronze brown
brassy gold, or iridescent blue-green and red; Chalcopyrite
H 3.5–4.0; Brittle; uneven fracture; Crystals:
tetrahedrons
SOFT Color characteristically brownish-bronze; Tarnishes
(H < 5.5) bright iridescent purple, blue, and/or red, giving It its
Dark gray nickname “peacock ore”; May be weakly attracted to Bornite
to black a magnet; H 3; Usually massive, rare as cubes or
Does not dodecahedrons
scratch glass
Color opaque brassy to brown-bronze; Tarnishes dull
Scratched by brown, may have faint iridescent colors; Fracture
masonry nail or uneven to conchoidal; No cleavage; Attracted to a
knife blade Cleavage magnet; H 3.5–4.5; Usually massive or masses of tiny Pyrrhotite
absent, crystals; Resembles chalcopyrite, which is softer and
poor, or not attracted to a magnet
not visible
Color dark silvery gray to black; Can be scratched
with your fingernail; Easily rubs off on your fingers and Graphite
clothes, making them gray; H 1–2
Metallic or silky submetallic luster, Color dark brown,
Yellow-brown gray, or black; H 5–5.5; Forms layers of radiating Goethite
microscopic crystals and botryoidal masses
Color copper; Tarnishes dull brown or green;
Copper H 2.5–3.0; Malleable and sectile; Hackly fracture; Copper (native copper)
Usually forms dendritic masses or nuggets
Color yellow gold; Does not tarnish; Malleable and
Gold sectile; H 2.5–3.0; Forms odd-shaped masses, Gold (native gold)
nuggets, or dendritic forms
Color silvery white to gray; Tarnishes gray to black;
Silvery white H 2.5–3.0; Malleable and sectile; Forms dendritic Silver (native silver)
masses, nuggets, or curled wires

FIGURE 3.18 Identification chart for opaque minerals with metallic or submetallic luster (M) on freshly broken surfaces.

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