Gahnite

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Gahnite
Gahnite.jpg
General
Category Oxide minerals
Spinel group
Spinel structural group
Formula
(repeating unit)
ZnAl2O4
IMA symbol Ghn [1]
Strunz classification 4.BB.05
Crystal system Cubic
Crystal class Hexoctahedral (m3m)
H-M symbol: (4/m 3 2/m)
Space group Fd3m
Identification
ColorDark green, bluish green, blue to indigo, yellow to brown
Crystal habit Typically octahedra, rarely as dodecahedra also massive to granular
Twinning Common on [111] produces striations
Cleavage Indistinct parting on [111]
Fracture Conchoidal, uneven
Mohs scale hardness7.5–8.0
Luster Vitreous
Streak Grey
Diaphaneity Translucent to nearly opaque
Specific gravity 4.38–4.60
Optical propertiesIsotropic
Refractive index n = 1.79–1.80
References [2] [3] [4]

Gahnite, ZnAl2O4, is a rare mineral belonging to the spinel group. It forms octahedral crystals which may be green, blue, yellow, brown or grey. It often forms as an alteration product of sphalerite in altered massive sulphide deposits such as at Broken Hill, Australia. Other occurrences include Falun, Sweden where it is found in pegmatites and skarns; and, in the United States, Charlemont, Massachusetts; Spruce Pine, North Carolina; White Picacho district, Arizona; Topsham, Maine; and Franklin, New Jersey. [2] [3]

It was first described in 1807 for an occurrence in the Falu mine, Falun, Dalarna, Sweden, and named after the Swedish chemist, Johan Gottlieb Gahn (1745–1818), the discoverer of the element manganese. [3] [4] It is sometimes called zinc spinel.

See also

Related Research Articles

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Albite is a plagioclase feldspar mineral. It is the sodium endmember of the plagioclase solid solution series. It represents a plagioclase with less than 10% anorthite content. The pure albite endmember has the formula NaAlSi
3
O
8
. It is a tectosilicate. Its color is usually pure white, hence its name from Latin, albus. It is a common constituent in felsic rocks.

<span class="mw-page-title-main">Clintonite</span>

Clintonite is a calcium magnesium aluminium phyllosilicate mineral. It is a member of the margarite group of micas and the subgroup often referred to as the "brittle" micas. Clintonite has the chemical formulaCa(Mg,Al)
3
(Al
3
Si)O
10
(OH)
2
. Like other micas and chlorites, clintonite is monoclinic in crystal form and has a perfect basal cleavage parallel to the flat surface of the plates or scales. The Mohs hardness of clintonite is 6.5, and the specific gravity is 3.0 to 3.1. It occurs as variably colored, colorless, green, yellow, red, to reddish-brown masses and radial clusters.

<span class="mw-page-title-main">Tephroite</span>

Tephroite is the manganese endmember of the olivine group of nesosilicate minerals with the formula Mn2SiO4. A solid solution series exists between tephroite and its analogues, the group endmembers fayalite and forsterite. Divalent iron or magnesium may readily replace manganese in the olivine crystal structure.

<span class="mw-page-title-main">Blödite</span> Sulfate mineral

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<span class="mw-page-title-main">Andradite</span> Nesosilicate mineral species of garnet

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Hausmannite is a complex oxide of manganese containing both di- and tri-valent manganese. The formula can be represented as Mn2+Mn3+2O4. It belongs to the spinel group and forms tetragonal crystals. Hausmannite is a brown to black metallic mineral with Mohs hardness of 5.5 and a specific gravity of 4.8.

<span class="mw-page-title-main">Trevorite</span>

Trevorite is a rare nickel iron oxide mineral belonging to the spinel group. It has the chemical formula NiFe3+2O4. It is a black mineral with the typical spinel properties of crystallising in the cubic system, black streaked, infusible and insoluble in most acids.

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9
(Mg,Fe3+
)(SiO
4
)
6
(SiO
3
OH)(OH)
3
. The cerium and lanthanum content varies with the Ce rich species and the La rich species. Analysis of a sample from the Mountain Pass carbonatite gave 35.05% Ce
2
O
3
and 30.04% La
2
O
3
.

<span class="mw-page-title-main">Hisingerite</span>

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Jacobsite is a manganese iron oxide mineral. It is in the spinel group and forms a solid solution series with magnetite. The chemical formula is (Mn,Mg)Fe2O4 or with oxidation states and substitutions: (Mn2+,Fe2+,Mg)(Fe3+,Mn3+)2O4.

<span class="mw-page-title-main">Brownmillerite</span> Rare calcium aluminium oxide mineral

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Grossite is a calcium aluminium oxide mineral with formula CaAl4O7. It is a colorless to white vitreous mineral which crystallizes in the monoclinic crystal system.

<span class="mw-page-title-main">Pyrophanite</span>

Pyrophanite is a manganese titanium oxide mineral with formula: MnTiO3. It is a member of the ilmenite group. It is a deep red to greenish black mineral which crystallizes in the trigonal system.

<span class="mw-page-title-main">Ferronigerite-2N1S</span>

Ferronigerite-2N1S is an iron, tin, alumino-hydroxide mineral that naturally occurs around sillimanite-quartz veins. Ferronigerite-2N1S belongs to the nigerite group, högbomite supergroup. The other constituents of the nigerite group are ferronigerite-6N6S, magnesionigerite-2N1S, magnesionigerite-6N6S, zinconigerite-2N1S and zinconigerite-6N6S. The 2N1S ending stands for the nolanite and spinel structural layers.

<span class="mw-page-title-main">Cuspidine</span>

Cuspidine is a fluorine bearing calcium silicate mineral (sorosilicate) with formula: Ca4(Si2O7)(F,OH)2. Cuspidine crystallizes in the monoclinic crystal system and occurs as acicular to spear shaped pale red to light brown crystals. It is a member of the wöhlerite group.

References

  1. Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi: 10.1180/mgm.2021.43 . S2CID   235729616.
  2. 1 2 Anthony, John W.; Bideaux, Richard A.; Bladh, Kenneth W.; Nichols, Monte C. (2005). "Gahnite" (PDF). Handbook of Mineralogy. Mineral Data Publishing. Retrieved 14 March 2022.
  3. 1 2 3 Gahnite, Mindat.org
  4. 1 2 http://webmineral.com/data/Gahnite.shtml Webmineral