Clintonite

Not to be confused with a political supporter of Bill Clinton, Hillary Clinton, or Clintonism.

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.

Clintonite
Clintonite with spinel on orthoclase matrix from Amity, New York (size: 9.3 × 5.7 × 3.8 cm)
General
Category	Phyllosilicate minerals, mica group
Formula	Ca(Mg,Al) 3(Al 3Si)O 10(OH) 2
IMA symbol	Cln[1]
Crystal system	Monoclinic
Crystal class	Prismatic (2/m) or domatic (m)
Space group	C2/m or (?)
Unit cell	a = 5.204 Å, b = 9.026 Å, c = 9.812 Å; β = 100.35°; Z = 2
Identification
Color	Colorless, yellow, orange, red-brown, brown, green
Crystal habit	Tabular pseudohexagonal crystals; foliated or lamellar radiated; massive
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	[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

• List of minerals
• List of minerals named after people