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Iron silicate mineral From Wikipedia, the free encyclopedia
Minnesotaite is an iron silicate mineral with formula: (Fe2+,Mg)3Si4O10(OH)2. It crystallizes in the triclinic crystal system and occurs as fine needles and platelets with other silicates.[2] It is isostructural with the pyrophyllite-talc mineral group.[3]
Minnesotaite | |
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General | |
Category | Silicate mineral |
Formula (repeating unit) | (Fe2+,Mg)3Si4O10(OH)2 |
IMA symbol | Mns[1] |
Strunz classification | 9.EC.05 |
Crystal system | Triclinic |
Crystal class | Pinacoidal (1) (same H-M symbol) |
Space group | P1 |
Unit cell | a = 5.623(2) Å, b = 9.419(2) Å, c = 9.624(3) Å; α = 85.21(3)°, β = 95.64(3)°, γ = 90.00°; Z = 2 |
Identification | |
Color | Greenish gray to olive-green |
Crystal habit | Occurs as microscopic needles or platelets, the needles occur in radiating clusters or in sheaves; also fibrous |
Twinning | Inferred based on X-ray patterns |
Cleavage | Perfect on {001}, micaceous |
Fracture | Uneven and irregular |
Tenacity | Brittle |
Mohs scale hardness | 1.5 - 2 |
Luster | Greasy to waxy, dull |
Diaphaneity | Translucent |
Specific gravity | 3.01 |
Optical properties | Biaxial (-) |
Refractive index | nα = 1.578 - 1.583 nβ = 1.578 - 1.622 nγ = 1.615 - 1.623 |
Birefringence | δ = 0.037 - 0.040 |
Pleochroism | X= pale green, Z= colorless to pale greenish yellow |
2V angle | Measured: 4° |
Dispersion | r < v moderate |
References | [2][3][4] |
Minnesotaite was first described in 1944 for occurrences in the banded iron formations of northern Minnesota for which it was named. Co-type localities are in the Cuyuna North Range, Crow Wing County and the Mesabi Range in St. Louis County.[3][5]
It occurs associated with quartz, siderite, stilpnomelane, greenalite and magnetite.[2][6] In addition to the low grade metamorphic banded iron formations it has also been reported as an alteration mineral associated with sulfide bearing veins.[3]
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