Chemical Formula Ca2Al2Si3O12(OH)
Color Green
Hardness 6 – 6.5
Crystal System Orthorhombic
Refractive Index 1.61 – 1.64
SG 2.8 – 3.0
Transparency Translucent
Double Refraction .030
Luster Vitreous, waxy
Cleavage 1,1;3,1
Mineral Class Prehnite

Prehnite has always been a minor collectors gemstone, but relatively recent deposits discovered in Africa containing facetable Prehnite in large quantities has made this gemstone more available and popular. Prehnite is very sensitive to heat and has perfect easily chips, so care must be exercised when cutting. Prehnite Cat’s Eyes do exist from the Australian finds, but these are very rare.


Prehnite is an inexpensive gemstone, and due its lack of full transparency it is usually cut into cabochons and beads. Other facets may be cut, but less commonly. Prehnite may also be carved into small ornamental objects such as flowers.


Prehnite gemstones are natural and not heated or artificially enhanced.

Prehnite SOURCES

Prehnite sources include Mali, South Africa, Namibia, Australia, China, and the U.S. (New Jersey).


Peridot – Slightly harder and usually more transparent.
Jade – Usually deeper in color and less transparent.
Pyrite, often called “Fools Gold”, has a silvery-yellow to golden metallic color. It is very common and may occur in large crystals. It has been used by ancient civilizations as jewelry, but is hardly used nowadays. Pyrite is sometimes incorrectly known as Marcasite in the gemstone trade. Marcasite is mineral that is a polymorph of Pyrite, and can be fragile and unstable, and is not fit for gemstone use.
Color Metallic, Yellow, Gray
Hardness 6 – 6.5
Crystal System Isometric
SG 4.9 – 5.2
Transparency Opaque
Double Refraction None
Luster Metallic
Cleavage None
Mineral Class Pyrite

Pyrite is used mostly as costume jewelry and as inexpensive beads. It is occasionally also carved into small roses, edge stones, and cabochons. Sometimes, perfect pyritohedral crystals are used in jewelry without being faceted. Aggregates of small sparkling natural Pyrite crystals are often used as a base material for ornamental figures.


Fool’s GoldPyrite is natural and not treated or enhanced.Pyrite is an extremely prevalent mineral and is found worldwide. Peru contains the most extensive deposits for collectors. Pyrope is the most well-known gemstone form of Garnet. The term Garnet describes a group name for several closely related minerals that form important gemstones, and Pyrope is an individual member mineral of the Garnet group. Its dark, blood-red color is distinct and attractive, and makes a fine Garnet gemstone. In the gem trade, the term Pyrope is rarely used on its own. It is either generically called “Garnet”, or “Pyrope Garnet”.

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