Larvikite
Augite Syenite (Monzonite) · Decorative Stone / Semi-Precious Gemstone
Crystal System
Triclinic/Monoclinic; commonly occurs as an igneous rock with a holocrystalline, coarse-grained texture rather than individual large crystals.
Mineral Group
Silicates (Tectosilicates); Feldspar family
Chemical Formula
(Na,K)AlSi3O8 (Significant ternary feldspar with inclusions of Magnetite or Ilmenite)
Formation Process
Igneous; it forms from the slow cooling of magma at great depths (plutonic), resulting in large, interlocking crystals of ternary feldspar.
About This Crystal
A dark, coarse-grained igneous rock characterized by large feldspar crystals that exhibit a blue or silver schiller. It is typically dark grey, charcoal, or bluish-black with visible patches of white/grey and black inclusions. It has a vitreous luster when polished.
Physical Characteristics
Color: Grey to black with blue/silver flashes; Streak: White; Cleavage: Perfect in two directions at nearly 90 degrees; Fracture: Conchoidal to uneven; Specific Gravity: 2.59 – 2.63; Fluorescence: Usually none; Magnetic: Often weakly magnetic due to trace magnetite.
Optical Properties
Refractive Index: 1.52 - 1.55; Birefringence: Low; Phenomenon: Schiller effect or 'labradorescence-like' adularescence caused by exsolution lamellae within the feldspars.
Hardness & Durability
Origin Region
Larvik region of Norway (Oslo Rift); specifically found in the Vestfold and Telemark counties.
Hardness & Durability
Mohs Hardness: 6 to 6.5; Toughness: Brittle; Stability: Good, though sensitive to strong acids.
Care & Maintenance
Clean with warm soapy water and a soft cloth; avoid ultrasonic cleaners and harsh chemicals. Store separately from harder gemstones like quartz or sapphire to prevent scratching.
Rarity & Value
Relatively common but geographically specific to Norway. Value is modest, determined by the intensity of the blue schiller and the quality of the polish.
Special Characteristics
Displays a unique optical flash called the Schiller effect; often contains inclusions of Ilmenite or Magnetite and sometimes Nepheline or Olivine.
Lore & History
Designated as the National Rock of Norway. Historically used as a prestigious building stone (e.g., United Nations building). In crystal lore, it is believed to be a stone of transformation, inner strength, and protection, often associated with the Root and Third Eye chakras.