Offretite

About it

Small six-sided prisms, often capping levyne or intergrown with erionite, in basalt cavities; first found at Mont Sémiol, France, and also known from Oregon and Germany's Vogelsberg.

Type

Mineral

Group

Silicate (tectosilicate), zeolite group

Formula

(K2,Ca)2.5Al5Si13O36·15H2O

Hardness (Mohs)

4

Specific gravity

2.13

Streak

white

Lustre

vitreous (glassy)

Crystal system

Hexagonal

Colours

colourless, white

Transparency

transparent, translucent

Cleavage and fracture

distinct basal

Typical values: real specimens vary. For more, see mindat.org.