Larvikite
Larvikite (Anorthoclase-rich Monzonite) · Decorative Stone / Semi-Precious Gemstone
Crystal System
Triclinic/Monoclinic; typically occurs as a massive, coarse-grained igneous rock (monzonite) rather than individual distinct crystals.
Mineral Group
Silicates (Tectosilicates); Feldspar group
Chemical Formula
(Na,K)AlSi3O8 (Significant components of Feldspar)
Formation Process
Igneous; forms via the slow cooling of magmatic intrusions deep in the crust (plutonic), allowing for coarse grain development.
About This Crystal
A dark, coarse-grained plutonic rock characterized by rhomb-shaped feldspar crystals. It exhibits a dark grey to bluish-black body color with a vitreous to pearly luster and a distinctive silvery-blue schiller effect called labradorescence (or ternary feldspar effect) when polished.
Physical Characteristics
Color: Dark grey, blue-grey to black; Streak: White; Cleavage: Perfect in two directions (feldspar component); Fracture: Uneven to conchoidal; Specific Gravity: 2.6 – 2.7; Tenacity: Brittle; Fluorescence: Generally inert.
Optical Properties
Refractive Index: 1.52-1.55; Birefringence: Low; Notable for the Schiller Effect (Labradorescence), an optical phenomenon caused by light scattering off internal exsolution lamellae within the feldspar crystals.
Hardness & Durability
Origin Region
Larvik region of Norway (Oslo Rift); also found in parts of Canada (Ontario).
Hardness & Durability
Mohs Hardness: 6 to 6.5. Good durability for decorative use and jewelry, though prone to scratching by quartz (Hardness 7). Good stability.
Care & Maintenance
Wash with warm soapy water and a soft cloth; avoid ultrasonic cleaners or harsh chemicals like hydrofluoric acid. Store separately to prevent scratching softer or harder stones.
Rarity & Value
Relatively common but geographically specific; valued for its unique optical flash. Generally affordable, with value determined by the intensity and coverage of the blue flash (Schiller).
Special Characteristics
Displays 'Schiller effect' or labradorescence due to the presence of perthitic intergrowths; often contains trace amounts of nepheline, augite, or magnetite which can make some specimens slightly magnetic.
Lore & History
Historically used as a prominent facing stone in architecture (e.g., the United Nations building). In metaphysical lore, it is referred to as 'Blue Pearl Granite' or 'Norwegian Moonstone' and is traditionally associated with grounding, protection, and enhancing psychic vision.