TrekGEO > Mineral Trail > Occurrence > Cristobalite zone

Japanese page

Cristobalite zone

Chemical Process (Alteration) - Open system under ground (Acidic-Neutral metasomatism)

Correlated: Low-T zeolite facies

Index Minerals


Required Geological Setting

Metasomatic rocks (Intermediate acidic)


Metasomatic zone formed by acidic-neutral hydrothermal fluid of 50-100 degree associated with Rhyolitic to Dacitic magma activities. This alteration is called cristobalitization. Protoliths are felsic rocks. Cristobalite zone may be associated with Hydrothermal Au-Ag deposits, Hot spring deposits or Hydrothermal deposits along faults. The water related to the alteration reaction of the cristobalite zone is meteoric water and/or magmatic water, and the water/rock ratio is more than a few tens times. It means that minerals were formed by reactions of the open system. On the other hand, the water related to the diagenesis is interstitial water in sediments, and the water/rock ratio is less than ten times. Minerals by diagenesis were formed by reactions of the closed system.

Cristobalite zone

Distribution of cristobalite zones described in this site. Yellow lines are volcanic fronts.

Change of mineral assemblages

  • [ Appear ] Cristobalite, Pyrite, Smectite

Mineral Assemblages

  • Cristobalite, Pyrite, Smectite, (Gypsum)


  • Akaze (Opal amygdules)
  • Hosaka (Opal amygdules)
  • Oiwa (Opal amygdules)
  • Su river (Gypsum deposit)

Related Occurrences

Copyright (c) 2015 NariNari, All Rights Reserved.