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 < br/>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

Meionite is a tectosilicate belonging to the scapolite group with the formula Ca₄Al₆Si₆O₂₄CO₃. Some samples may also contain a sulfate group. It was first discovered in 1801 on Mt Somma, Vesuvius, Italy.