Feldspar
Feldspar Group Mineral · Mineral Specimen and Rock-Forming Mineral
Crystal System
Monoclinic or Triclinic, typically forming massive or tabular habits
Mineral Group
Silicates (Tectosilicates)
Chemical Formula
KAlSi3O8 - NaAlSi3O8 - CaAl2Si2O8
Formation Process
Igneous crystallization in magmas and pegmatites, as well as metamorphic processes
About This Crystal
An opaque to translucent earthy mineral specimen with irregular shape, showing mottled grey, white, and brownish weathering tones with a pearly to vitreous luster on cleavage planes
Physical Characteristics
Color ranges from white, grey, to tan and pink; white streak; perfect cleavage in two directions at or near 90 degrees; uneven to conchoidal fracture; specific gravity around 2.5 to 2.7; brittle tenacity
Optical Properties
Biaxial with low birefringence; refractive index ranges from 1.52 to 1.54; may exhibit adularescence or labradorescence depending on the specific feldspar variety
Hardness & Durability
Origin Region
Found globally in igneous, metamorphic, and sedimentary rocks; major deposits in the USA, Brazil, Madagascar, and Norway
Hardness & Durability
Mohs hardness of 6; moderate toughness but vulnerable to perfect cleavage planes; fair wearability for jewelry with protective settings
Care & Maintenance
Clean with warm soapy water and a soft brush; avoid harsh chemicals, ultrasonic cleaners, and sudden thermal shock
Rarity & Value
Common, as feldspar makes up over 60 percent of the Earth's crust; low to moderate value for standard mineral specimens unless cut as a specific gemstone variety like labradorite or moonstone
Special Characteristics
Displays characteristic right-angle cleavage planes and potential optical phenomena such as adularescence or plagioclase twinning
Lore & History
Historically recognized as a foundational rock-forming mineral group essential to human ceramic and glass production; in modern metaphysical practices, feldspar is often associated with self-discovery, new beginnings, and vitality