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Class: Silicates
Group: Scapolite

Typically in regionally metamorphosed rocks, especially marbles, calcareous gneisses; also in skarns, some pegmatites, pneumatolytically or hydrothermally altered mafic igneous rocks, and ejected volcanic blocks (Anthony et al., 2001—2005).
Petschite — specimen 0081
Petschite — specimen 0081, photo © NMNHS

Original description: ‘Màrialith’ vom Rath, G., 1866. 5. Mineralogisch-geognostische Fragmente aus Italien — Zeitschrift der Deutschen Geologischen Gesellschaft 18: 636—637 [view in ‘Library’].

Type locality: Pianura, Phlegrean Fields, Naples Province, Campania, Italy.

Type material: unknown.

Etymology: named by Gerhard vom Rath in honour of his wife, Maria Rosa vom Rath.

Distribution: Brazil: Minas Gerais; Canada; Italy: Pianura, west of Naples, Campania; Madagascar; Mexico; Myanmar: Mogok district; Russia: near Lake Baikal, Siberia; Tanzania (Anthony et al., 2001—2005).



Essential elements: oxygen (O), sodium (Na), aluminium (Al), silicon (Si), chlorine (Cl).

Crystal data

Crystallography: tetragonal — dipyramidal. Crystal habit: crystals prismatic, typically with flat pyramidal terminations, striated, to 1.5 m; granular, massive (Anthony et al., 2001—2005).

Physical properties

Cleavage: {100}, {110}, distinct (Anthony et al., 2001—2005). Fracture: uneven to conchoidal (Anthony et al., 2001—2005). Tenacity: brittle (Anthony et al., 2001—2005). Hardness: 5.5—6 (Anthony et al., 2001—2005). Density: 2.5—2.62 g/cm3 (Anthony et al., 2001—2005). Luminescence: commonly fluoresces orange to bright yellow or red under LW or SW UV (Anthony et al., 2001—2005).

Optical properties

Colour: colourless, white, grey, pink, violet, blue, yellow, brown, orange-brown; colourless in thin section (Anthony et al., 2001—2005). Diaphaneity: transparent to opaque (Anthony et al., 2001—2005). Lustre: vitreous, pearly, resinous (Anthony et al., 2001—2005). Refractive index: 1.539—1.55 — anisotropic [uniaxial (-)] (Anthony et al., 2001—2005). Birefringence: 0.004—0.008. Dispersion: none. Pleochroism: none.

Material from ‘Repository’

8 specimens: 0097 — 2.78 ct, Namibia; 0195 — 1.11 ct, Tanzania; 0196 — 1.47 ct, Tanzania; 0255 — 0.39 ct, Tanzania; 0081 — 0.20 ct, Tanzania; 0082 — 0.30 ct, Tanzania; 0334 — 0.22 ct, Tanzania; 0335 — 0.19 ct, Tanzania.

Gallery view