What is Prehnite?


Prehnite is a translucent to transparent gem-quality hydrated calcium aluminum silicate. It was the first mineral to be named after an individual, and it was first discovered in South Africa in 1774. Prehnite is often used as a gemstone and is a popular choice for collectors due to its unique green color.

Prehnite is a translucent gemstone that comes in shades of green and yellow. Its unique appearance and color make it a popular choice for jewelry and decorative items, especially rings and pendants.

Gemstone Properties

Chemical ClassificationInorganic - Silicate
ColorMost commonly a soft, pastel green, but can also be yellow, blue, or colorless.
LusterVitreous to pearly.
TransparencyTranslucent to transparent.
OccurrenceSouth Africa, Australia, and China.
FormationTypically found in the cavities of basalt rocks, and sometimes in granites or gneisses.
DiaphaneityTransparent to translucent
Mohs Hardness6 to 6.5
Specific Gravity2.80 - 2.95
Diagnostic PropertiesPale green, often in botryoidal masses.
Chemical CompositionCa2Al(AlSi3O10)(OH)2
PleochroismWeak; colors can vary based on viewing angle.
Crystal SystemOrthorhombic
Optical PropertiesBiaxial (+)
Refractive Index1.610 - 1.635
Birefringence0.020 - 0.022
2V angleMeasured: 85° to 90°
DispersionNot typically noted for its dispersion.