Celestine (mineral)

Celestine
Clear grey-blue celestine crystals
General
Category	Sulfate minerals
Formula (repeating unit)	SrSO4 sometimes contains minor calcium and/or barium
IMA symbol	Clt[1]
Strunz classification	7.AD.35
Crystal system	Orthorhombic
Crystal class	Dipyramidal (mmm) H-M symbol: (2/m 2/m 2/m)
Space group	Pnma
Unit cell	a = 8.359 Å, b = 5.352 Å, c = 6.866 Å; Z = 4
Identification
Color	White, pink, pale green, pale brown, black, pale blue, reddish, greyish; colourless or lightly tinted in transmitted light
Crystal habit	Tabular to pyramidal crystals, also fibrous, lamellar, earthy, massive granular
Cleavage	Perfect on {001}, good on {210}, poor on {010}
Fracture	Uneven
Tenacity	Brittle
Mohs scale hardness	3.0–3.5
Luster	Vitreous, pearly on cleavages
Streak	white
Diaphaneity	Transparent to translucent
Specific gravity	3.95–3.97
Optical properties	Biaxial (+)
Refractive index	nα = 1.619–1.622 nβ = 1.622–1.624 nγ = 1.630–1.632
Birefringence	δ = 0.011
Pleochroism	Weak
2V angle	Measured: 50°–51°
Dispersion	Moderate r < v
Ultraviolet fluorescence	yellow, white blue (both short and long UV)
References	[2][3][4][5]

Celestine (the IMA-accepted name)^[6] or celestite^[1][7][a] is a mineral consisting of strontium sulfate (SrSO₄). The mineral is named for its occasional delicate blue color. Celestine and the carbonate mineral strontianite are the principal sources of the element strontium, commonly used in fireworks and in various metal alloys.

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