Hauyne

Hauyne, haüyne or hauynite is a tectosilicate mineral with sulfate and chloride with formula: (Na,Ca)4-8Al6Si6(O,S)24(SO4,Cl)1-2. It is a feldspathoid and a member of the sodalite group. Hauyne crystallizes in the isometric system forming translucent, vitreous typically twinned crystals with highly variable color (blue, white, grey, yellow, green, pink). It has a Mohs hardness of 5 to 6 and a specific gravity of 2.4 to 2.5.
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General Information:
 Chemical Formula:
(Na,Ca)4-8Al6Si6(O,S)24(SO4,Cl)1-2
 Composition:
(Molecular Weight = 1,032.43 gm)
Sodium 8.91 % Na
Calcium 7.76 % Ca
Aluminum 15.68 % Al
Silicon 16.32 % Si
Sulfur 9.32 % S 
Chlorine 1.72 % Cl
Oxygen 40.29 % O 
 Empirical Formula:
Na4Ca2Al6Si6O22S2(SO4)Cl0.5
 Environment:
Igneous rocks low in silica and rich in alkalies.
 Locality:
Vesuvian lavas, on Mte Somma, Italy.
 Name Origin:
Named after the French crystallographer, R. J. Hauy (1743-1822).
Physical Properties:
 Cleavage:
[110] Perfect, [011] Perfect, [101] Perfect
 Color:
blue, green, red, yellow, or gray.
 Density:
2.4 - 2.5, Average = 2.45
 Diaphaniety:
Subtransparent to translucent
 Habits:
Crystalline - Coarse - Occurs as well-formed coarse sized crystals., Twinning Common - Crystals are usually twinned., Euhedral Crystals - Occurs as well-formed crystals showing good e xternal form.
 Hardness:
5-6 - Between Apatite and Orthoclase
 Luminescence:
None.
 Luster:
Vitreous - Greasy
 Streak:
bluish white
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