Outstanding colorless and yellow crystals (tinted of yellow by selenium) of the extremely rare ammonium silicofluoride minerals baratite and cryptohalite from a locality in Pennsylvania ( Northumberland County, Pennsylvania, United States of America). Ex Vandenbroucke Museum collection from Waregem, Belgium. — Photo: David Hospital · CC BY-SA 4.0
Cryptohalite
The rare cubic mineral form of ammonium fluorosilicate — a toxic fumarole encrustation.
Intro adapted from Wikipedia (CC BY-SA).
Cryptohalite is an IMA-recognized mineral species in the halide class, with the chemical formula (NH₄)₂SiF₆.
It crystallizes in the cubic crystal system (space group Fm3m).
Key properties: Mohs hardness 2.5; specific gravity 2.004; Vitreous luster.
IMA symbol Cphl, grandfathered status — known before the IMA’s founding, named in 1874.
A volcanic sublimate, or formed from fires in burning coal seams.
It is found associated with Sal ammoniac, bararite, sulfur, selenium.
Its name comes from the Greek for concealed and salt, for being admixed with sal ammoniac.