Gismondine
Mineral Ca2Al4Si4O16·9H2O
Also called Gismondine-Ca and Gismondite
About it
Crystals that look like square double pyramids (really twinned monoclinic forms) in basalt and leucite lavas; named for Carlo Gismondi, with its type locality near Rome, Italy.
- Type
- Mineral
- Group
- Silicate (tectosilicate), zeolite group
- Formula
- Ca2Al4Si4O16·9H2O
- Hardness (Mohs)
- 4.5
- Specific gravity
- 2.2–2.26
- Streak
- white
- Lustre
- vitreous (glassy)
- Crystal system
- Monoclinic
- Colours
- colourless, white, grey, bluish white, reddish
- Transparency
- transparent, translucent
- Cleavage and fracture
- distinct in one direction
Typical values: real specimens vary. For more, see mindat.org.