Scapolite group | |
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General | |
Category | Tectosilicates |
IMA symbol | Scp[1] |
Crystal system | Tetragonal |
Identification | |
Color | Pink, red, blue, brown, white, grey, colourless, green, yellow, orange, purple |
Cleavage | Good, in 2 directions |
Fracture | Conchoidal, uneven, brittle |
Mohs scale hardness | 5.5–6 |
Luster | Vitreous |
Streak | White |
Diaphaneity | Opaque to transparent |
Specific gravity | 2.6–2.74 |
Optical properties | Uniaxial (–) |
Refractive index | nω = 1.555–1.594 nε = 1.526–1.565 |
Birefringence | 0.004–0.038 |
Pleochroism | Moderate to strong |
Dispersion | 0.017 |
Ultraviolet fluorescence | Inert to strong pink, orange and yellow |
The scapolites (Greek: σκάπος, "rod", and λίθος, "stone") are a group of rock-forming silicate minerals composed of aluminium, calcium, and sodium silicate with chlorine, carbonate and sulfate. The two endmembers are meionite (Ca4Al6Si6O24CO3)[2] and marialite (Na4Al3Si9O24Cl).[3][4] Silvialite (Ca,Na)4Al6Si6O24(SO4,CO3) is also a recognized member of the group.[5][4][6]