Larvikite
Monzonite (intermediate igneous rock containing Anorthoclase and Albite) · Semi-Precious Gemstone / Decorative Stone
Crystal System
Triclinic/Monoclinic; traditionally found as massive, coarse-grained plutonic rock
Mineral Group
Silicates (Tectosilicates); Feldspar Group
Chemical Formula
(Na,K)AlSi3O8 (primarily Anorthoclase/Albite with trace Augite and Magnetite)
Formation Process
Igneous; formed through deep-seated magmatic crystallization of alkalic monzonite (plutonic)
About This Crystal
Polished crescent-shaped stone with a grey to dark-grey base color. It features a vitreous luster and distinct black inclusions (likely Augite or Hornblende) and exhibits a characteristic blue or silver flash known as schiller effect.
Physical Characteristics
Color: Grey to black; Streak: White; Cleavage: Two directions at nearly 90 degrees; Fracture: Uneven to conchoidal; Specific Gravity: 2.59–2.63; Fluorescence: Weak to none.
Optical Properties
Displays 'labradorescence' or schiller effect (peristerite/adularescence-like flash) due to microscopic exsolution lamellae; Refractive Index: 1.520–1.550; Biaxial.
Hardness & Durability
Origin Region
Larvik Fjord region, Norway (Oslo Rift); also found in Ontario, Canada
Hardness & Durability
Mohs hardness: 6–6.5; Toughness: Brittle; Fair durability for jewelry but susceptible to scratching by quartz.
Care & Maintenance
Avoid harsh chemicals and ultrasonic cleaners; clean with warm soapy water and a soft cloth; store separately to prevent scratching.
Rarity & Value
Common/Abundant; value is relatively low and determined by the intensity of the blue flash/schiller; rarely treated.
Special Characteristics
Presents a 'schiller' effect or 'labradorescence' which is an optical phenomenon producing silver or blue flashes across surface grains.
Lore & History
Commonly known as 'Black Moonstone' or 'Norwegian Moonstone' (though not a true moonstone). Traditionally associated with ground energy, protection, and patience in folklore; designated as the National Stone of Norway.