Mineral Identification Key

The Mineral Identification Key

Copper, Michigan, Seaman Museum specimen

Table IC: Metallic or Submetallic Luster and Hardness greater than 5½: (Can not be scratched by a knife.) [Previous Table] [Next Table]

Hardness Color Streak Cleavage Name System Habit SG Notes

4 to 5½ Black or
Dark greenish or Yellowish-brown Pale yellowish or Brownish BETAFITE
(Ca,Na,U)₂(Ti,Nb)O₆(OH) Isometric Massive (metamict) Approx. 4 to 6 (variable) Luster usually sub-metallic, but may be resinous to vitreous, highly radioactive

5 to 5½ Pale Copper-red to Pinkish Silvery-white, tarnishing to Dark-grey or Black Black NICKELINE
NiAs 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,
color black in ferberite, brown in hübnerite Dark-brown to Black One perfect direction FERBERITE/
HÜBNERITE
("Wolframite" series)
(Fe,Mn)WO₄(Mn,Fe)WO₄ Monoclinic Usually massive, granular, crystals tabular to bladed with vertical striations 7.0 to 7.5
above about 7.3 indicates ferberite, lower indicates hübnerite Streak darkens with increasing Fe content

5 to 5½ Dark-brown to Black Yellow-brown or Yellow-ocher One perfect direction GOETHITE
(pronounced "Ger-ta-ite.")
FeO(OH) Orthorhombic Usually in radiating botryoidal aggregates, mammillary, or stalactic 4.37

5 to 5½ Dark-brown to Black, Dark yellowish-brown to Greenish-brown, Dark reddish-brown Pale yellowish or Brownish MICROLITE
(Na,Ca)₂Ta₂O₆(O,OH,F) Isometric Usually massive,
granular, crystals octahedral 5.90-6.42 Luster usually resinous to vitreous, but when resinous may appear sub-metallic, may contain some U and be radioactive

5 to 5½ Brown to Black or Dark yellowish-brown Light-brown to Yellowish-brown PYROCHLORE
(Na,Ca)₂Nb₂O₆(OH,F)·nH₂O Isometric Usually massive, granular, crystals usually octahedral, modified by the cube 4.45-4.90 Luster usually resinous to vitreous, but when resinous may appear sub-metallic, usually contains some U and is radioactive Distinguished from microlite by its lower S.G.

Hardness Color Streak Cleavage Name System Habit SG Notes

5 to 6 Black Black to Dark-brown ROMANECHITE
(Ba,H₂O)₂(Mn⁴⁺Mn³⁺)₅O₁₀ Orthorhombic Usually massive, botryoidal or stalactic 3.7 to 4.7 Distinguished from similar Mn minerals by its greater hardness

5 to 6 Black to Silvery-black Black to Dark-brown ILMENITE
FeTiO₃ Trigonal Usually as platy massive or granular, crystals rare, thick tabular or acute rhombohedral 4.72 May be weakly magnetic

5 to 6 Deep blood-red Black to Dark-brown or Reddish-brown Perfect in two directions PYROPHANITE
MnTiO₃ Trigonal Usually in fine-grained, scaly, masses 4.54

Hardness Color Streak Cleavage Name System Habit SG Notes

5½ Tin-white or Silvery-white Black One perfect direction COBALTITE/
GERSDORFFITE
(Co,Ni)AsS
(Ni,Co)AsS Isometric Usually massive, granular, cubic and pyritohedral crystals (cobaltite) or octahedral and pyritohedral crystals (gersdorffite) 6.3
(cobaltite),
5.9
(gersdorffite) Difficult to distinguish end members without chemical tests, S.G. may help for samples close to the ideal end members.

5½ Tin-white or Silvery-white Black Two distinct directions, poor in one direction SKUTTERUDITE/
NICKEL-SKUTTERUDITE
(Co,Ni)As_2-3(Ni,Co,)As_2-3 Isometric Usually massive, crystals cubes or cubo-octahedral 6.5
to 6.9
(skutterudite – nickel-skutterudite) High end S.G. indicates the skutterudite end member, otherwise difficult to distinguish from one another.

5½ Black Black to Dark-brown URANINITE
UO₂ Isometric Usually massive 9.0 to 9.7 ("Pitchblende"), luster actually "pitchy", may be botryoidal, radioactive

5½ Brownish-black Dark-brown CHROMITE
FeCr₂O₄ Isometric Usually massive, granular 4.6 Luster actually "pitchy", often with green alteration products

5½ Pale copper-red Red-brown BREITHAUPTITE
NiSb Hexagonal Usually massive, crystals rare, tabular 7.59 to 8.23 Rare

5½ to 6 Tin-white or Silvery-white, tarnishing Brown or Bronzish Black One distinct direction ARSENOPYRITE
FeAsS Monoclinic Usually massive, granular, crystals pseudo-orthorhombic prismatic, usually in cruciform twins or star-shaped trillings 6.0 to 6.2 Has garlic odor when ground or pounded – poisonous arsenic fumes

5½ to 6 Brown, Yellowish-brown, Reddish-brown; Dark-brown to Iron-black; White to Grayish-white or Yellowish-white One indistinct direction BROOKITE
TiO₂ Orthorhombic Usually tabular, elongated and striated crystals, commonly pyramidal or pseudohexagonal 4.08 to 4.18 Found in alpine veins in gneiss and schist. Also found in contact metamorphic and hydrothermal veins

5½ to 6 Brown, Yellowish-brown, Reddish-brown, Indigo, Black; Geenish, Pale lilac, Gray, rarely Colorless White to Pale yellow Two perfect directions ANATASE
TiO₂ Tetragonal Usually pyramidal or tabular 3.79 to 3.97 Found in alpine veins in gneiss and schist as a secondary mineral.

5½ to 6 Dark-brown to Steel-grey to Black Rust-red or Indian-red HEMATITE
Fe₂O₃ Trigonal Usually massive in radiating, reniform, or micaceous aggregates, crystals rhombohedral 4.8 to 5.3 Usually black and usually harder than a knife. (See under Sections IA & IB.)

Hardness Color Streak Cleavage Name System Habit SG Notes

6 Black Black MAGNETITE
Fe₃O₄ Isometric Massive or in octahedral crystals 5.18 Strongly magnetic

6 Black Black to Dark-brown One distinct direction COLUMBITE/
TANTALITE
(Fe,Mn)(Nb,Ta)₂O₆ Orthorhombic Usually massive platy, or as thick tabular crystals 5.2 to 6.76
(ferrocolumbite)
7.95
(ferrotantalite) A complex solid solution series exists within the Columbite-Group; distinguishing between species is difficult without subtle chemical tests. S.G. may be indicative for some species but not definitive. Columbite/tantalite series is now broken down into the four end-member minerals - ferrocolumbite, manganocolumbite, ferrotantalite and manganotantalite

6 Brownish-black Dark-brown FRANKLINITE
(Fe,Zn,Mn)(Fe,Mn)₂O₄ Isometric Usually massive, granular, or as octahedral crystals 5.15 May be slightly magnetic. Rare outside of Franklin, N.J., USA

Hardness Color Streak Cleavage Name System Habit SG Notes

6 to 6½ Brass-yellow Black (may be greenish-black) PYRITE
FeS₂ Isometric Massive or in striated cubic, pyritohedral, or octahedral crystals, may be twinned 5.0 Most common brass-yellow metallic mineral

6 to 6½ Brass-yellow Black (may be greenish-black) One distinct direction MARCASITE
FeS₂ Orthorhombic Usually massive, granular, crystals usually "cockscomb" clusters or radiating fibrous aggregates 4.9 Difficult to distinguish from pyrite without tests unless good crystals are present.

6 to 6½ Dark-brown to Black Pale-brown One distinct direction RUTILE
TiO₂ Tetragonal Usually in prismatic crystals, vertically striated, often needle-like as inclusions in silicate crystals, particularly quartz 4.2 to 4.25 Anatase and brookite are closely related species, but rarer.

Note: The Betafite-Microlite-Pyrochlore Group and Subgroups are complex, species can be difficult to tell apart. S.G. and radioactivity may be indicative for some species, but are rarely definitive.
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Hardness	Color	Streak	Cleavage	Name	System	Habit	SG	Notes
4 to 5½	Black or Dark greenish or Yellowish-brown	Pale yellowish or Brownish		BETAFITE (Ca,Na,U)₂(Ti,Nb)O₆(OH)	Isometric	Massive (metamict)	Approx. 4 to 6 (variable)	Luster usually sub-metallic, but may be resinous to vitreous, highly radioactive
5 to 5½	Pale Copper-red to Pinkish Silvery-white, tarnishing to Dark-grey or Black	Black		NICKELINE NiAs	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, color black in ferberite, brown in hübnerite	Dark-brown to Black	One perfect direction	FERBERITE/ HÜBNERITE ("Wolframite" series) (Fe,Mn)WO₄(Mn,Fe)WO₄	Monoclinic	Usually massive, granular, crystals tabular to bladed with vertical striations	7.0 to 7.5 above about 7.3 indicates ferberite, lower indicates hübnerite	Streak darkens with increasing Fe content
5 to 5½	Dark-brown to Black	Yellow-brown or Yellow-ocher	One perfect direction	GOETHITE (pronounced "Ger-ta-ite.") FeO(OH)	Orthorhombic	Usually in radiating botryoidal aggregates, mammillary, or stalactic	4.37
5 to 5½	Dark-brown to Black, Dark yellowish-brown to Greenish-brown, Dark reddish-brown	Pale yellowish or Brownish		MICROLITE (Na,Ca)₂Ta₂O₆(O,OH,F)	Isometric	Usually massive, granular, crystals octahedral	5.90-6.42	Luster usually resinous to vitreous, but when resinous may appear sub-metallic, may contain some U and be radioactive
5 to 5½	Brown to Black or Dark yellowish-brown	Light-brown to Yellowish-brown		PYROCHLORE (Na,Ca)₂Nb₂O₆(OH,F)·nH₂O	Isometric	Usually massive, granular, crystals usually octahedral, modified by the cube	4.45-4.90	Luster usually resinous to vitreous, but when resinous may appear sub-metallic, usually contains some U and is radioactive Distinguished from microlite by its lower S.G.
Hardness	Color	Streak	Cleavage	Name	System	Habit	SG	Notes
5 to 6	Black	Black to Dark-brown		ROMANECHITE (Ba,H₂O)₂(Mn⁴⁺Mn³⁺)₅O₁₀	Orthorhombic	Usually massive, botryoidal or stalactic	3.7 to 4.7	Distinguished from similar Mn minerals by its greater hardness
5 to 6	Black to Silvery-black	Black to Dark-brown		ILMENITE FeTiO₃	Trigonal	Usually as platy massive or granular, crystals rare, thick tabular or acute rhombohedral	4.72	May be weakly magnetic
5 to 6	Deep blood-red	Black to Dark-brown or Reddish-brown	Perfect in two directions	PYROPHANITE MnTiO₃	Trigonal	Usually in fine-grained, scaly, masses	4.54
Hardness	Color	Streak	Cleavage	Name	System	Habit	SG	Notes
5½	Tin-white or Silvery-white	Black	One perfect direction	COBALTITE/ GERSDORFFITE (Co,Ni)AsS (Ni,Co)AsS	Isometric	Usually massive, granular, cubic and pyritohedral crystals (cobaltite) or octahedral and pyritohedral crystals (gersdorffite)	6.3 (cobaltite), 5.9 (gersdorffite)	Difficult to distinguish end members without chemical tests, S.G. may help for samples close to the ideal end members.
5½	Tin-white or Silvery-white	Black	Two distinct directions, poor in one direction	SKUTTERUDITE/ NICKEL-SKUTTERUDITE (Co,Ni)As_2-3(Ni,Co,)As_2-3	Isometric	Usually massive, crystals cubes or cubo-octahedral	6.5 to 6.9 (skutterudite – nickel-skutterudite)	High end S.G. indicates the skutterudite end member, otherwise difficult to distinguish from one another.
5½	Black	Black to Dark-brown		URANINITE UO₂	Isometric	Usually massive	9.0 to 9.7	("Pitchblende"), luster actually "pitchy", may be botryoidal, radioactive
5½	Brownish-black	Dark-brown		CHROMITE FeCr₂O₄	Isometric	Usually massive, granular	4.6	Luster actually "pitchy", often with green alteration products
5½	Pale copper-red	Red-brown		BREITHAUPTITE NiSb	Hexagonal	Usually massive, crystals rare, tabular	7.59 to 8.23	Rare
5½ to 6	Tin-white or Silvery-white, tarnishing Brown or Bronzish	Black	One distinct direction	ARSENOPYRITE FeAsS	Monoclinic	Usually massive, granular, crystals pseudo-orthorhombic prismatic, usually in cruciform twins or star-shaped trillings	6.0 to 6.2	Has garlic odor when ground or pounded – poisonous arsenic fumes
5½ to 6	Brown, Yellowish-brown, Reddish-brown; Dark-brown to Iron-black;	White to Grayish-white or Yellowish-white	One indistinct direction	BROOKITE TiO₂	Orthorhombic	Usually tabular, elongated and striated crystals, commonly pyramidal or pseudohexagonal	4.08 to 4.18	Found in alpine veins in gneiss and schist. Also found in contact metamorphic and hydrothermal veins
5½ to 6	Brown, Yellowish-brown, Reddish-brown, Indigo, Black; Geenish, Pale lilac, Gray, rarely Colorless	White to Pale yellow	Two perfect directions	ANATASE TiO₂	Tetragonal	Usually pyramidal or tabular	3.79 to 3.97	Found in alpine veins in gneiss and schist as a secondary mineral.
5½ to 6	Dark-brown to Steel-grey to Black	Rust-red or Indian-red		HEMATITE Fe₂O₃	Trigonal	Usually massive in radiating, reniform, or micaceous aggregates, crystals rhombohedral	4.8 to 5.3	Usually black and usually harder than a knife. (See under Sections IA & IB.)
Hardness	Color	Streak	Cleavage	Name	System	Habit	SG	Notes
6	Black	Black		MAGNETITE Fe₃O₄	Isometric	Massive or in octahedral crystals	5.18	Strongly magnetic
6	Black	Black to Dark-brown	One distinct direction	COLUMBITE/ TANTALITE (Fe,Mn)(Nb,Ta)₂O₆	Orthorhombic	Usually massive platy, or as thick tabular crystals	5.2 to 6.76 (ferrocolumbite) 7.95 (ferrotantalite)	A complex solid solution series exists within the Columbite-Group; distinguishing between species is difficult without subtle chemical tests. S.G. may be indicative for some species but not definitive. Columbite/tantalite series is now broken down into the four end-member minerals - ferrocolumbite, manganocolumbite, ferrotantalite and manganotantalite
6	Brownish-black	Dark-brown		FRANKLINITE (Fe,Zn,Mn)(Fe,Mn)₂O₄	Isometric	Usually massive, granular, or as octahedral crystals	5.15	May be slightly magnetic. Rare outside of Franklin, N.J., USA
Hardness	Color	Streak	Cleavage	Name	System	Habit	SG	Notes
6 to 6½	Brass-yellow	Black (may be greenish-black)		PYRITE FeS₂	Isometric	Massive or in striated cubic, pyritohedral, or octahedral crystals, may be twinned	5.0	Most common brass-yellow metallic mineral
6 to 6½	Brass-yellow	Black (may be greenish-black)	One distinct direction	MARCASITE FeS₂	Orthorhombic	Usually massive, granular, crystals usually "cockscomb" clusters or radiating fibrous aggregates	4.9	Difficult to distinguish from pyrite without tests unless good crystals are present.
6 to 6½	Dark-brown to Black	Pale-brown	One distinct direction	RUTILE TiO₂	Tetragonal	Usually in prismatic crystals, vertically striated, often needle-like as inclusions in silicate crystals, particularly quartz	4.2 to 4.25	Anatase and brookite are closely related species, but rarer.