Prehnite
Prehnite · Semi-Precious Gemstone / Mineral Specimen
Crystal System
Orthorhombic; typically occurs in botryoidal, globular, or stalactitic habits, often as radiating fibrous aggregates.
Mineral Group
Silicates (Phyllosilicate subgroup)
Chemical Formula
Ca2Al(AlSi3O10)(OH)2
Formation Process
Hydrothermal mineral occurring in cavities and veins of mafic volcanic rocks (basalt, diabase); also forms in low-grade metamorphic rocks.
About This Crystal
A translucent to semi-transparent pale green to yellow-green stone with a characteristic 'oily' or pearly luster. This specific tumbled specimen displays a distinctive dark inclusion, likely Epidote, which is a common association for Prehnite.
Physical Characteristics
Color: Pale green to yellow-green; Streak: White; Cleavage: Good in one direction; Specific Gravity: 2.80–2.95; Fluorescence: Occasionally weak yellow or orange under UV light.
Optical Properties
Biaxial positive; Refractive Index: 1.611–1.669; Birefringence: 0.022–0.033; No significant pleochroism.
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 toughness; reasonably durable for jewelry but sensitive to heavy pressure and heat.
Care & Maintenance
Clean with warm soapy water and a soft brush. Avoid ultrasonic cleaners, steam cleaning, and harsh household chemicals. Store away from harder gemstones like quartz or sapphire to prevent scratching.
Rarity & Value
Relatively common; value is determined by color intensity (saturation), clarity, and the presence of aesthetically pleasing inclusions like Epidote needles.
Special Characteristics
Commonly contains needle-like or dark chlorite/epidote inclusions creating a 'mossy' look. Often displays a unique velvety or 'hazy' internal glow when polished.
Lore & History
Historically significant as the first mineral to be named after an individual (Colonel Hendrik Von Prehn) in 1788. In metaphysical lore, it is known as the 'Stone of Unconditional Love' and is associated with the Heart Chakra.