4 Photos
Clintonite
Chemical Formula	Ca(Mg,Al)3(Al3Si)O10(OH)2
Species	Silicates
Crystal System	Monoclinic
Mohs Scale	4-5
Specific Gravity	3.0-3.1
Color	Colorless, yellow, orange, red-brown, brown, green
Streak	White, slightly yellow-gray
Luster	Vitreous, pearly, submetallic
Refractive Index	n = 1.643 - 1.648 n = 1.655 - 1.662 n = 1.655 - 1.663
Diaphaneity	Transparent to translucent
Cleavage	Perfect on
Crystal Habit：Tabular pseudohexagonal crystals; foliated or lamellar radiated; massive

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.

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.

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