Prehnite
Prehnite · Semi-Precious Gemstone / Collector Mineral
Crystal System
Orthorhombic; typically occurs in botryoidal, globular, or stalactitic habits. Individual crystals are rare and usually tabular or prismatic.
Mineral Group
Silicates; Subgroup: Phyllosilicates (Sheet silicates), though the structure is often considered a framework silicate (Tectosilicate).
Chemical Formula
Ca2Al(AlSi3O10)(OH)2
Formation Process
Hydrothermal mineral forming in the cavities (vesicles) of volcanic rocks and fissures in basaltic or gabbroic rocks. Forms under low-to-medium pressure and temperature conditions.
About This Crystal
This specimen is a small, polished light-green stone with a characteristic 'greasy' to vitreous luster. It exhibits a translucent to semi-opaque appearance with a pale, yellowish-green hue typical of the mineral.
Physical Characteristics
Color: Pale green to yellow-green; Streak: White; Cleavage: Good in one direction (distinctly basal); Fracture: Irregular to conchoidal; Specific Gravity: 2.80 - 2.95; Tenacity: Brittle; Fluorescence: May show weak yellow or blue under SW/LW UV light.
Optical Properties
Refractive Index: 1.611 - 1.669; Birefringence: 0.022 - 0.033; Pleochroism: Weak to absent; Optical Character: Biaxial (+). Often exhibits a cloudy or hazy appearance due to microscopic fibrous inclusions.
Hardness & Durability
Origin Region
Notable sources include South Africa (Cape Province), Australia (Northern Territory), Mali, USA (New Jersey), and Scotland. Found in mafic volcanic rocks and low-grade metamorphic zones.
Hardness & Durability
Mohs Hardness: 6.0 - 6.5. It is relatively tough but the cleavage makes it susceptible to damage if struck hard. Suitable for jewelry with protective settings like pendants or earrings.
Care & Maintenance
Clean with warm soapy water and a soft brush. Avoid ultrasonic and steam cleaners. Store away from harder stones like quartz or corundum to prevent scratching. Sensitive to high heat and acids.
Rarity & Value
Relatively common; Value is determined by color intensity (vibrant green is preferred), transparency, and the presence of aesthetic inclusions like black epidote needles. Generally affordable for collectors.
Special Characteristics
Known for its 'inner glow' and sometimes referred to as 'Cape Chrysolite.' In rare instances, it can exhibit chatoyancy. Often found associated with Zeolites or Epidote.
Lore & History
Historically named after Colonel Hendrik Von Prehn in 1788, the first mineral named after a person. Traditionally associated with the Heart Chakra, it is often called the 'stone of unconditional love' and believed in lore to enhance intuition and dream recall.