These other forms of silica include opal, chalcedony, flint and chert (non-crystalline), and cristobalite, tridymite, coesite, and stichovite.    From Wordnik.com.  [Quartz] Reference

But they were surprised to find cristobalite and tridymite.    From Wordnik.com.  [News and Features - NASA's Jet Propulsion Laboratory] Reference

The crystals, called cristobalite and tridymite, are known to reside in comets, in volcanic lava flows on Earth, and in some meteorites that land on Earth.    From Wordnik.com.  [News and Features - NASA's Jet Propulsion Laboratory] Reference

It is this high-temperature form of silica crystals, specifically cristobalite and tridymite, that Forrest's team found in planet-forming disks around other stars for the first time.    From Wordnik.com.  [News and Features - NASA's Jet Propulsion Laboratory] Reference

It is these high-temperature forms of silica crystals, specifically cristobalite and tridymite, that Forrest's team found in planet-forming disks around other stars for the first time.    From Wordnik.com.  [SPACE.com] Reference