Clintonite

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(Al
3Si)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.

Not to be confused with a political supporter of Bill Clinton or Hillary Clinton.
Clintonite
Clintonite with spinel on orthoclase matrix from Amity, New York (size: 9.3 x 5.7 x 3.8 cm)
General
CategoryPhyllosilicate mica group
Formula
(repeating unit)		Ca(Mg,Al)
3(Al
3Si)O
10(OH)
2
IMA symbolCln[1]
Crystal systemMonoclinic
Crystal classPrismatic (2/m)
or domatic (m)
Space groupC2/m or (?)
Unit cella = 5.204 Å,
b = 9.026 Å,
c = 9.812 Å;
β = 100.35°; Z = 2
Identification
ColorColorless, yellow, orange, red-brown, brown, green
Crystal habitTabular pseudohexagonal crystals; foliated or lamellar radiated; massive
TwinningSpiral polysynthetic twinning
CleavagePerfect on {001}
TenacityBrittle
Mohs scale hardness3.5 on {001}, 6 at angle to {001}
LusterVitreous, pearly, submetallic
StreakWhite, slightly yellow-gray
DiaphaneityTransparent to translucent
Specific gravity3.0 - 3.1
Optical propertiesBiaxial (-)
Refractive indexnα = 1.643 - 1.648 nβ = 1.655 - 1.662 nγ = 1.655 - 1.663
Birefringenceδ = 0.012 - 0.015
PleochroismX = colorless, pale orange, red-brown; Y = Z = pale brownish yellow, pale green
2V angleMeasured: 2° to 40°
References[2][3][4][5]

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.[6] Clintonite and its iron-rich variety xanthophyllite are sometimes considered the calcium analogues of the phlogopites.[7]

Typical formation environment is in serpentinized Dolomitic limestone and contact metamorphosed skarns. It occurs with talc, spinel, grossular, vesuvianite, clinopyroxene, monticellite, chondrodite, phlogopite, chlorite, quartz, calcite and dolomite.[5]

Clintonite was first described in 1843 for an occurrence in Orange County, New York. It was named for De Witt Clinton (1769–1828).[4]

See also

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. Mineralienatlas
  3. Webmineral
  4. Mindat with location data
  5. Handbook of Mineralogy
  6. One or more of the preceding sentences incorporates text from a publication now in the public domain: Spencer, Leonard James (1911). "Clintonite". In Chisholm, Hugh (ed.). Encyclopædia Britannica. Vol. 6 (11th ed.). Cambridge University Press. p. 530.
  7. 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.
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