Bytownite
Image: James St. John (CC BY 2.0)
Mineral NameBytownite
Chemical Formula(Ca,Na)Al(Si,Al)Si2O8, with Ca dominant (An70-90)
Mohs Hardness6
Crystal Systemtriclinic
Lustervitreous
Streak Colorwhite
Cleavageperfect in two directions (pinacoidal), nearly at 90 degrees (86-87°)
Fractureuneven to conchoidal
Specific Gravity2.7
Colorswhite, gray, yellowish, greenish
Transparencytransparent to translucent
Type LocalityWiborg Batholith, Kymi Province, Finland
Mineral GroupSilicates (Tectosilicates, Feldspar Group, Plagioclase Series)
Usescollector's specimens, scientific research
Associated Mineralspyroxene, olivine, amphibole, magnetite, other feldspars
Raritycommon
Description
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.
Geological 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.
