Image: James St. John (CC BY 2.0)
tricliniccommonSilicates (Tectosilicates, Feldspar Group, Plagioclase Series)
Bytownite
(Ca,Na)Al(Si,Al)Si2O8, with Ca dominant (An70-90)
Bytownite is a grayish-white to yellowish mineral, often occurring as granular masses or tabular crystals. The specimen in the image, though identified as Bytownite, displays a strong iridescent play of colors (labradorescence), which is more commonly associated with labradorite.
Bytownite Physical Properties
Mohs Hardness
6Crystal System
triclinicLuster
vitreousStreak Color
whiteCleavage
perfect in two directions (pinacoidal), nearly at 90 degrees (86-87°)Fracture
uneven to conchoidalSpecific Gravity
2.7Colors
white, gray, yellowish, greenishTransparency
transparent to translucentType Locality
Wiborg Batholith, Kymi Province, FinlandMineral Group
Silicates (Tectosilicates, Feldspar Group, Plagioclase Series)Uses
collector's specimens, scientific researchAssociated Minerals
pyroxene, olivine, amphibole, magnetite, other feldsparsRarity
commonGeological Context
Bytownite is a common rock-forming mineral found primarily in mafic igneous rocks such as gabbro, basalt, and anorthosite, crystallizing from high-temperature magmas. It can also occur in some high-grade metamorphic rocks.
