The Mineral Identification Key Copper, Michigan, Seaman Museum specimen

Table IA:  Minerals with Metallic or Submetallic Luster &  Hardness of less than 2½: (Will readily leave a mark on paper.)  [Next Table
Hardness Color Streak Cleavage Name System Habit SG Notes
1+ Dark-red to Vermilion Rust-red   HEMATITE
Fe2O3
Trigonal Ocherous masses, granular, often as a pigment – "rust" – in rocks 5.2 Exhibits a wide range of hardness depending on form; crystalline hematite is harder.
1 to 1½ Steel-grey to Iron-black Black One perfect direction (basal) GRAPHITE
C
Trigonal May be in small hexagonal plates 2.23 Has a greasy feel.
1 to 1½ Bluish-black Black to Greenish-black One perfect direction (basal) MOLYBDENITE  MoS2 Trigonal Usually in somewhat foliated appearing masses, often leaf-like hexagonal plate 4.7 Has a greasy feel; heavier than graphite
Hardness Color Streak Cleavage Name System Habit SG Notes
1 to 2 Iron-black Black One perfect direction PYROLUSITE
MnO2
Tetragonal May be splintery or in  radiating fibrous masses 4.7 Sometimes won’t mark paper. Most dendrites are not pyrolusite.
Lead-grey Lead-grey One perfect direction NAGYÁGITE
Pb5Au(Te,Sb)4S5-8
Orthorhombic pseudo-
tetragonal
Usually platy masses, may be granular 7.4 to 7.5 Flakes flexible.  Rare.
Steel-grey Steel-grey One perfect direction TETRADYMITE
Bi2Te2S
Trigonal Usually in foliated to bladed masses, acute rhombohedral crystals rare 7.1 to 7.4 Flexible.  Relatively rare.
1½ to 2 Silvery-white Grey   SYLVANITE
(Au,Ag)2Te4
Monoclinic Usually granular or in bladed aggregates, often appears as skeletal forms on rocks, resembling writing (cuneiform). 8 to 8.2 May not mark paper. Rare.
Hardness Color Streak Cleavage Name System Habit SG Notes
2 Grey-black to Lead-grey Black to Grey-black One perfect direction, two imperfect BISMUTHINITE Bi2S3 Orthorhombic In bladed crystals showing cross striations 6.78 Similar to stibnite but heavier.  Rare
2 Grey-black Bluish-black to Silvery-black One perfect direction (prismatic), two imperfect STIBNITE
Sb2S3
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,  sometimes won’t mark paper.
2 to 2½ Grey-black to Lead-grey Black   ACANTHITE
Ag2S
Isometric Pseudo-cubic,  usually massive 7.3 Bright-steel-grey on fresh surfaces but darkens upon exposure, easily cut with a knife (sectile).  Sometimes won’t mark paper
2 to 2½ Iron-black Iron-black   STEPHANITE
Ag5SbS4
Orthorhombic Usually massive, more rarely as short prismatic to tabular crystals 6.2 to 6.5 Rare
Hardness Color Streak Cleavage Name System Habit SG Notes
2 to 2½ Bright-red Bright-red to Deep-red One perfect direction CINNABAR
HgS
Trigonal Usually in granular masses 8.1 Luster actually adamantine, sometimes appearing sub-metallic to metallic. May not mark paper.
2 to 2½ Brownish-red to Scarlet or Vermilion Deep Ruby-red to Bright Ruby-red One distinct direction PYRARGYRITE/ PROUSTITE
Ag3(Sb,As)S3
Ag3(As,Sb)S3
Trigonal Prismatic, pyramidal, rhombohedral, and scalenohedral crystals , also massive, usually as complex intergrown crystal aggregates 5.57 to 5.58 Isostructural species difficult to distinguish, though pyrargyrite is usually darker in color and more common than proustite. Rare.
2 to 2½ Silvery-white Silvery-white with decidedly reddish tones One perfect direction (basal), one good  BISMUTH
Bi
Trigonal Usually in laminated granular masses, may be arborescent or reticulated, artificial crystals in pseudo-cubic "hopper" groups 9.8 Heavy. Rare. May not mark paper.
Hardness Color Streak Cleavage Name System Habit SG Notes
Brass-yellow to Silvery-white Yellowish- to Greenish-grey   CALAVERITE
AuTe2
Monoclinic Usually granular, rarely in distinct elongated crystals 9.35 Very heavy, easily fusible in candle flame (leaving globules of gold). (May not mark paper.)  Rare.
Grey-black to Black Bluish-black to Lead-grey Perfect in three directions at 90o to each other GALENA
PbS
Isometric Usually in cubic crystals or masses exhibiting cubic cleavage, also in granular masses. 7.6 Sometimes won’t mark paper
2 to 3 Black Black One imperfect direction POLYBASITE
(Ag,Cu)16Sb2S11
Monoclinic, pseudo-
hexagonal
Usually massive or in crude pseudo-hexagonal plates 6.1 to 6.2 Rare

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