Meionite

Meionite
	Meionite (scapolite) crystals (cross-shaped) in a quartz matrix, 7.2 x 4.0 x 3.0 cm. Worcester County, Massachusetts.
General
Category	Tectosilicate ; Scapolite group
Formula; (repeating unit)	Ca4Al6Si6O24CO3
Strunz classification	9.FB.15
Crystal system	Tetragonal
Crystal class	Dipyramidal (4/m) ; (same H-M symbol)
Space group	I4/m
Unit cell	a = 12.179(1) Å, ; c = 7.571(1) Å, Z = 2
Identification
Color	Colorless, white, grey, pink, violet, blue, yellow, orange-brown, brown
Cleavage	Distinct/good on {100}{110}
Fracture	Irregular/uneven, conchoidal
Tenacity	Brittle
Mohs scale hardness	5 - 6
Luster	Vitreous, resinous, pearly
Streak	White
Diaphaneity	Transparent, opaque
Specific gravity	2.74 - 2.78
References	[1][2][3][4]

Meionite is a tectosilicate belonging to the scapolite group with the formula Ca₄Al₆Si₆O₂₄CO₃.[5] Some samples may also contain a sulfate group. It was first discovered in 1801 on Mt Somma, Vesuvius, Italy. It was named by Rene Just Haüy after μειωυ, the Greek word for less, in reference to the less acute pyramidal form as compared to Vesuvianite.

References

Mineralienatlas
Mindat.org
Webmineral.com
Handbook of Mineralogy
Teertstra, David K.; Sherriff, Barbara L. (1997-04-25). "Substitutional mechanisms, compositional trends and the end-member formulae of scapolite". Chemical Geology. 136 (3): 233–260. doi:10.1016/S0009-2541(96)00146-5. ISSN 0009-2541.

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[1] Mineralienatlas

[2] Mindat.org

[3] Webmineral.com

[4] Handbook of Mineralogy

[5] Teertstra, David K.; Sherriff, Barbara L. (1997-04-25). "Substitutional mechanisms, compositional trends and the end-member formulae of scapolite". Chemical Geology. 136 (3): 233–260. doi:10.1016/S0009-2541(96)00146-5. ISSN 0009-2541.