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Clintonite

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Clintonite

Clintonite
Clintonite with spinel on orthoclase matrix from Amity, New York (size: 9.3 x 5.7 x 3.8 cm)
General
Category Phyllosilicate Mica group
Formula
(repeating unit)
Ca(Mg,Al)3(Al3Si)O10(OH)2
Crystal symmetry Monoclinic 2/m - prismatic
Unit cell a = 5.204Å, b = 9.026Å, c = 9.812Å; β = 100.35°; Z = 2
Identification
Color Colorless, yellow, orange, red-brown, brown, green
Crystal habit Tabular pseudohexagonal crystals; foliated or lamellar radiated; massive
Crystal system Monoclinic
Twinning Spiral polysynthetic twinning
Cleavage Perfect on {001}
Tenacity Brittle
Mohs scale hardness 3.5 on {001}, 6 at angle to {001}
Luster Vitreous, pearly, submetallic
Streak White, slightly yellow-gray
Diaphaneity Transparent to translucent
Specific gravity 3.0 - 3.1
Optical properties Biaxial (-)
Refractive index nα = 1.643 - 1.648 nβ = 1.655 - 1.662 nγ = 1.655 - 1.663
Birefringence δ = 0.012 - 0.015
Pleochroism X = colorless, pale orange, red-brown; Y = Z = pale brownish yellow, pale green
2V angle Measured: 2° to 40°
References [1][2][3]

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 formula: Ca(Mg,Al)3(Al3Si)O10(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.

The brittle micas differ chemically from the micas in containing less silica and no alkalis, and from the chlorites in containing much less water; in many respects, they are intermediate between the micas and chlorites. Clintonite and its iron-rich variety xanthophyllite are sometimes considered the calcium analogues of the phlogopites.[4]

Typical formation environment is in serpentinized dolomitic limestones and contact metamorphosed skarns. It occurs with talc, spinel, grossular, vesuvianite, clinopyroxene, monticellite, chondrodite, phlogopite, chlorite, quartz, calcite and dolomite.[3]

Clintonite was first described in 1843 for an occurrence in Orange County, New York. It was named for De Witt Clinton (1769–1828).[2]

See also

References

  1. ^ Webmineral
  2. ^ a b Mindat with location data
  3. ^ a b Handbook of Mineralogy
  4. ^ Alietti, Elisa, et al., Clintonite-1M: Crystal chemistry and its relationships to closely associated Al-rich phlogopite, American Mineralogist, Volume 82, pages 936–945, 1997. [2]
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