The Mineral Identification Key Copper, Michigan, Seaman Museum specimen

Table IB: Minerals with Metallic or Submetallic Luster & Hardness greater than 2½, but less than 5½: (Will not easily mark paper, but can be scratched with a pocket knife.) [Previous Table [Next Table
Hardness Color Streak Cleavage Name System Habit SG Notes
1 to 2 Iron-black Black One perfect direction PYROLUSITE
Tetragonal May be splintery or in radiating fibrous masses 4.7 Will sometimes mark paper.
1½ to 2 Silvery-white Grey   SYLVANITE
Monoclinic Usually granular or in bladed aggregates, often appears as skeletal forms on rocks, resembling writing (cuneiform) 8 to
May mark paper.
1½ to 2 Metallic-blue, tarnishes to blue-black Black One perfect direction (basal) COVELLITE
Trigonal Platy masses or thin six-sided platy crystals 4.6 May be somewhat iridescent, turns metallic-purple when wet. Will sometimes mark paper.
Hardness Color Streak Cleavage Name System Habit SG Notes
2 Bluish-black to Silvery-black Grey-black One perfect direction (prismatic), two imperfect STIBNITE
Orthorhombic Usually as thick bladed crystals with striations both parallel to and across the long axis; crystals often bent or "kinked" 4.5 Fuses in a candle flame. Will sometimes mark paper.
2 to 2½ Deep Ruby-red to Bright Ruby-red Brownish-red to Scarlet or Vermilion One distinct direction PYRARGYRITE/ PROUSTITE 
Trigonal Prismatic, pyramidal, rhombohedral, and scalenohedral crystals , also massive, usually as complex intergrown crystal aggregates 5.58 (pyrargyrite), 5.57 (proustite) Isostructural species difficult to distinguish, though pyrargyrite is usually darker in color and more common than proustite, fusible in a candle flame. Rare.
2 to 2½ Grey-black to Lead-grey Black   ACANTHITE
Isometric Pseudo-cubic, usually massive 7.3 Bright steel-grey on fresh surfaces but darkens upon exposure, easily cut with a knife (sectile). Will usually mark paper.
Hardness Color Streak Cleavage Name System Habit SG Notes
Bluish-black to Lead-grey Grey-Black to Black Perfect  in three directions at 90o to each other GALENA
Isometric Usually in cubic crystals or masses exhibiting cubic cleavage, also in granular masses 7.6 Will usually mark paper. Most common heavy mineral.
Brass-yellow to Silvery-white Yellowish to Greenish-grey   CALAVERITE
Monoclinic Usually granular, rarely in distinct elongated crystals 9.35 Very heavy, easily fusible in a candle flame (leaving globules of gold). May mark paper. Rare.
2 to 3 Grey-black Black One good direction JAMESONITE
Monoclinic Dense clusters or carpets of fibrous to acicular crystals; very delicate! 5.5 to 6.0 Fuses easily in a candle flame.
Hardness Color Streak Cleavage Name System Habit SG Notes
2½ to 3 Grey-black Grey to Black   BOURNONITE
Orthorhombic Usually in stout prismatic crystals often as intergrown clusters with twinning exhibited by re-entrant angles 5.8 to 5.9 Fuses easily in a candle flame
2½ to 3 Steel-grey, may tarnish to black on exposure Grey to Black   CHALCOCITE
Monoclinic, pseudo-
Usually in compact masses, crystals tabular to stoutly prismatic, often with a pseudo-hexagonal outline, vertically striated. 5.7  
2½ to 3 Dark metallic Blue to Black Black   DIGENITE
Isometric Usually massive as small to tiny irregular grains, very rarely as octahedral crystals 5.5 to 5.7 Very similar to chalcocite, but much rarer in non-microscopic sizes.
2½ to 3 Steel-grey, tarnishes metallic blue Dark steel-grey   STROMEYERITE
Orthorhombic, pseudo-
Usually massive, granular, rarely as pseudo-hexagonal prismatic crystals 6.2 to 6.3 Rare.
Hardness Color Streak Cleavage Name System Habit SG Notes
2½ to 3 Lead-grey Brown to brownish-grey One distinct direction BOULANGERITE
Monoclinic Usually massive as fibrous bundles, crystals usually needle-like mats, prismatic crystals rarer 6.0 to 6.3 Thin acicular crystals flexible. Rare.
2½ to 3 Dark-red to Vermilion Dark-red One perfect direction CINNABAR
Trigonal Usually massive, crystals uncommon and usually rhombohedral, often as penetration twins 8.10 Luster actually adamantine, appearing metallic, heavy.
2½ to 3 Copper-red on fresh surfaces, tarnishes to brown or black Coppery-red, shiny   COPPER
Isometric Usually in irregular masses, large grains, wires, and crude dendritic crystals, crystals usually octahedral and malformed, may be cubic or other Isometric forms 8.9 Malleable.
2½ to 3 Golden-yellow, shiny, becoming paler with increased Ag content - electrum variety Golden-yellow, shiny   GOLD
Isometric Usually massive in irregular grains, nuggets, "leaves" and "flakes", crystals often wires crudely dendritic or as malformed octahedrons 15.0 to 19.3 Malleable, very heavy! Rare. Distinguished from pyrite – "fools gold" – by its malleability, softness and weight.
2½ to 3 Silvery-white,
tarnishes black
Silvery-white, shiny   SILVER
Isometric Usually massive as irregular grains,  wires, and dendritic crystals 10.5 Malleable, heavy. Rare.  May mark paper.
Hardness Color Streak Cleavage Name System Habit SG Notes
3 Grey-black Black One perfect (prismatic), two distinct, and one indistinct direction ENARGITE
Orthorhombic Usually in bladed masses 4.4 Crystals vertically striated
3 Brownish-bronze on fresh surfaces, tarnishing to metallic purple, iridescent ("peacock ore") Grey-black   BORNITE
Crystals usually pseudo-cubic, usually massive 5.1 Thin splinters fusible in a candle flame, giving a brittle magnetic globule.
3 to 3½ Brass-yellow Black, sometimes with a greenish tinge   MILLERITE
Trigonal Usually in radiating groups or mats of needle-like to hair-like crystals 5.5 Slender crystals usually have a greenish tinge
3 to 3½ Steel-grey Steel-grey One indistinct direction ZINKENITE
Hexagonal Usually massive, also in columnar and radiating fibrous aggregates of needle-like crystals 5.2 to 5.3 Rare
3 to 3½ Tin-white Silvery-grey, shiny One perfect, one distinct, and one imperfect direction ANTIMONY
Trigonal Usually massive, foliated, or granular, rarely as pseudo-cubic or thick tabular crystals 6.6 to 6.7 Very brittle. Rare
Hardness Color Streak Cleavage Name System Habit SG Notes
3 to 4½ Steel-grey, may tarnish dead black upon exposure Black (may be Brownish-black)   TETRAHEDRITE/
Isometric Usually massive or granular, crystals uncommon and usually pseudo-tetrahedral 4.6 to 5.1 End members difficult to distinguish without subtle tests – an S.G. above 4.7 is conclusive for tetrahedrite.
Tin-white, tarnishing to Dark-grey Grey-black One perfect (basal) ARSENIC
Trigonal Usually found in botryoidal fibrous masses 5.7 Heated in candle flame it gives off white fumes that have a strong garlic odor (poisonous!) Rare
3½ to 4 Brownish-bronze to Bronze-yellow Black No cleavage but large grains exhibit an octahedral parting PENTLANDITE
Isometric Usually massive in granular aggregates 4.6 to 5.0 Resembles pyrrhotite but is not magnetic, often mixed with pyrrhotite
3½ to 4 Brass-yellow, often iridescent Black   CHALCOPYRITE
Tetragonal Usually massive, crystals blocky tetrahedrons or wedge-shaped. 4.1 to 4.3 Often mixed with pyrite, making a hardness test inconclusive; distinguished from pyrite by softness and shape of crystals.
3½ to 4 Brown to Black Brown Good  in one direction, poor in another direction WURTZITE
Hexagonal Usually massive and as banded botryoidal crusts, more rarely as pyramidal hemimorphic crystals 4.0 to 4.1 Rare
Hardness Color Streak Cleavage Name System Habit SG Notes
3½ to 4 Dark-brown to black, sometimes Olive-yellow or Red ("Ruby Jack") to Reddish-black Dark to Light-brown: streak usually lighter than the color of the sample Perfect  in six directions, three directions usually prominent SPHALERITE
Isometric Usually in compact crystalline masses, crystals usually blocky pyramidal, appearing tetrahedral 3.9 to 4.1 Luster actually resinous, appearing metallic or submetallic
3½ to 4 Ruby-red to Reddish-brown Brownish-red   CUPRITE
Isometric Usually massive, crystals usually cubes or octahedrons 6.0 Luster may be adamantine rather than metallic in crystals
3½ to 4 Black Green One perfect direction ALABANDITE
Isometric Usually massive or granular. 4.0 to 4.1 Rare
Hardness Color Streak Cleavage Name System Habit SG Notes
4 Brownish-bronze to Bronze-yellow Grey-black   PYRRHOTITE
Usually massive, crystals as pseudo-hexagonal plates 4.6 to 4.7 Magnetic, though may be weak
4 Steel-grey to Iron-black Black Indistinct  in two directions STANNITE
Tetragonal Usually massive, rarely as pseudo-octahedral crystals 4.3 to 4.5 Rare
4 Steel-grey to Iron-black Dark reddish-brown to Black One perfect, two good directions MANGANITE
Monoclinic, pseudo-
Usually in radiating fibrous masses, crystals often grouped in bundles. 4.3 Often associated with pyrolusite; distinguished from that species by its significantly greater hardness
4 to 4½ White to Steel-grey Grey, shiny   PLATINUM
Isometric Usually massive in irregular grains or nuggets, crystals rare and usually malformed cubes 14 to 19 Malleable, very heavy!  Very rare. Distinguished from gold by its color.
Hardness Color Streak Cleavage Name System Habit SG Notes
5 Steel-grey Black One perfect direction GLAUCODOT
Orthorhombic Usually massive, more rarely as prismatic crystals in cruciform penetration twins 5.9 to 6.1 Rare; alloclasite, monoclinic, is dimorphous with glaucodot and difficult to distinguish from it, but is probably even rarer
5 Yellowish or reddish-brown Pale-brown to white Variable: may be good in one direction and poor to good in another direction MONAZITE
Monoclinic Usually massive, granular, may be in crude large crystals 4.6 to 5.3 (approx.) Luster usually resinous to waxy, but may be adamantine and may appear sub-metallic
5 to 5½ Dark-brown to Black:  color black in ferberite brown in hübnerite Dark-brown to Black: streak darkens with increasing Fe content One perfect direction FERBERITE/
("Wolframite" series)

Monoclinic Usually massive, granular, crystals tabular to bladed with vertical striations 7.0 to 7.5 S.G. above about 7.3 indicates ferberite, lower indicates hübnerite
5 to Pale Copper-red to Pinkish silvery-white, tarnishing to Dark-grey or Black Black   NICKELINE
Hexagonal Usually massive, crystals rare and usually pyramidal, often malformed, may also be reticulated or arborescent 7.78 May be coated with green "nickel bloom" (annabergite).
5 to 5½ Dark brown to Black Yellow-brown or Yellow-ocher One perfect direction GOETHITE
(pronounced "Ger-ta-ite.")
Orthorhombic Usually in radiating botryoidal aggregates, mammillary, or stalactic 4.37  
Hardness Color Streak Cleavage Name System Habit SG Notes
Dark-brown to Black Iron-black to Brownish-black   CHROMITE

(Magnesiochromite is closely related, S.G. 4.2, Rare.
Manganochromite, H. 6½, is even rarer.)

Isometric Usually massive, rarely as octahedral crystals 4.6 Luster usually pitchy, submetallic, usually associated with peridotite rocks and accompanied by green or yellow alteration products.
5½ to 6½ Dark-brown to Steel-grey to Black Rust-red or Indian-red   HEMATITE
Trigonal Usually massive in radiating, reniform, or micaceous aggregates 4.8 to 5.3 Usually harder than a knife, but some forms can be softer. (See under Tables IA & IC.)

Return to Step 3

[ Table of Contents ] [ Introduction ] [ Identification Kit ] [ Mineral Properties ] [ Environments & Associations ] [ In Conclusion ] [ The Mineral ID Key ]

[Previous Table [Next Table