Prehnite
Prehnite with Schorl or Epidote inclusions · Semi-Precious Gemstone / Mineral Specimen
Crystal System
Orthorhombic; typically forms in globular, botryoidal, or stalactitic habits, often found as tumbled stones in commercial trade.
Mineral Group
Silicates (Phyllosilicate subgroup)
Chemical Formula
Ca2Al(AlSi3O10)(OH)2 with trace Fe3+ colorants
Formation Process
Secondary or hydrothermal mineral forming in cavities of mafic volcanic rocks (basalt), often occurring as a result of low-grade metamorphism.
About This Crystal
Translucent to semi-transparent pale green to yellow-green stones with a distinctive pearly to vitreous luster. These specimens feature prominent dark green to black needle-like inclusions of Epidote or Schorl (Tourmaline).
Physical Characteristics
Color: Apple-green to oil-green; Streak: White; Cleavage: Good in one direction; Fracture: Irregular to subconchoidal; Specific Gravity: 2.80–2.95; Fluorescence: Weakly fluorescent under UV (yellow or pinkish).
Optical Properties
Refractive Index: 1.611–1.669; Birefringence: 0.022–0.035; Optical Character: Biaxial positive; Phenomenon: Often exhibits a 'cloudy' or 'milky' internal glow.
Hardness & Durability
Origin Region
Prominent sources include South Africa (Cape Province), Australia (Wave Hill), Mali, and the USA (New Jersey).
Hardness & Durability
Mohs Hardness: 6 to 6.5. Brittle tenacity makes it susceptible to impact; suitable for pendants or earrings, but requires protective settings for rings.
Care & Maintenance
Clean with warm soapy water and a soft cloth; avoid ultrasonic cleaners and steam cleaners. Sensitive to high heat and strong acids.
Rarity & Value
Relatively common and affordable. Value is determined by the clarity of the green body color and the aesthetic arrangement of the dark needle inclusions.
Special Characteristics
Features characteristic 'epidote needles' or dark tourmaline-like inclusions that create a high-contrast aesthetic against the pale green matrix.
Lore & History
Historically named after Colonel Hendrik Von Prehn in 1788 (the first mineral named after a person). Traditionally associated with the heart chakra and known in lore as a 'stone of dreaming' and spiritual connection.