Apophyllite
Apophyllite group
Uncommon · KCa₄Si₈O₂₀(F,OH)·8H₂O
A hydrated potassium calcium silicate forming glassy prismatic crystals associated with zeolites in basaltic rocks. Its high water content causes it to exfoliate when heated. Frequently displays attractive combinations with stilbite and heulandite.
Identity
- Formula
- KCa₄Si₈O₂₀(F,OH)·8H₂O
- Chemical class
- Silicate
- Members
- Fluorapophyllite-(K), Hydroxyapophyllite-(K)
- Also known as
- Fluorapophyllite, Hydroxyapophyllite
Crystallography
- Crystal system
- Tetragonal
- Habits
- Prismatic, Tabular, Pyramidal
- Fracture
- Uneven
Physical properties
- Mohs hardness
- 4.5
- Density
- 2.35 g/cm³
- Luster
- Vitreous, Pearly
- Colors
- colorless, white, green, pink, yellow
- Streak
- white
- Transparency
- Transparent, Translucent
Geology
- Origins
- Hydrothermal
- Host rocks
- Granite, Volcanic rock, Marble
- Associated minerals
- Stilbite, Heulandite, Calcite, datolite
- Found in
- Skarn
- Geography
- India (Pune region), USA, Brazil, Germany, Iceland
Classification
- Rarity
- Uncommon
- Gem quality
- No
Sources
- Apophyllite Group. Mindat.org (Hudson Institute of Mineralogy).
- M. Pasero and others, IMA Commission on New Minerals, Nomenclature and Classification, The New IMA List of Minerals, updated September 2026. International Mineralogical Association (CNMNC), 2026.
- J. W. Anthony, R. A. Bideaux, K. W. Bladh, M. C. Nichols, Fluorapophyllite. Mineral Data Publishing, Handbook of Mineralogy, 2001.
- Apophyllite Group. Gemdat.org (Hudson Institute of Mineralogy).
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