Smoky Quartz in Feldspar Matrix
Quartz var. Smoky (SiO2) within Orthoclase/Microcline (KAlSi3O8) · Mineral Specimen / Decorative Stone
Crystal System
Quartz: Trigonal (Hexagonal trapezohedral class). Feldspar: Monoclinic or Triclinic. Habit in this specimen is massive and blocky.
Mineral Group
Silicates (Tectosilicates). Quartz is in the silica group; Feldspar is in the feldspar group.
Chemical Formula
SiO2 (Quartz) and KAlSi3O8 (Potassium Feldspar). Silicon dioxide with traces of aluminum and irradiation in the quartz; Potassium aluminum silicate in the feldspar.
Formation Process
Igneous/Pegmatitic formation. Forms from the slow cooling of magma where volatile-rich fluids allow large crystals of quartz and feldspar to intergrow.
About This Crystal
Blocky, opaque to translucent tan-colored feldspar matrix containing embedded pockets of gray to black translucent smoky quartz. The quartz exhibits a vitreous luster, while the feldspar is pearly to dull.
Physical Characteristics
Color: Tan/Peach (Feldspar) and Smoky Gray (Quartz). Streak: White for both. Fracture: Conchoidal (Quartz) and Uneven (Feldspar). Cleavage: Perfect in two directions for feldspar; none for quartz.
Optical Properties
Quartz is doubly refractive (uniaxial positive) with a refractive index of 1.544-1.553. Feldspar has an RI of 1.518-1.526. No significant pleochroism visible in this rough state.
Hardness & Durability
Origin Region
Common sources include Brazil, Colorado (Pikes Peak), and Madagascar. Found in granitic pegmatites and metamorphic environments.
Hardness & Durability
Quartz is 7 on Mohs scale; Feldspar is 6. Generally durable, but feldspar can split along cleavage planes if struck. Moderate toughness.
Care & Maintenance
Wash with warm soapy water. Avoid ultrasonic cleaners if hidden fractures exist. Quartz can slightly fade if exposed to harsh, direct sunlight for years.
Rarity & Value
Common. This is a standard mineral specimen of petrogenic minerals. Value is nominal, primarily for educational or decorative interest.
Special Characteristics
Displays intergrowth of two distinct minerals. Often exhibits weak fluorescence under UV if certain trace elements are present in the feldspar matrix.
Lore & History
Smoky quartz is historically considered a grounding stone in various cultures. In folklore, it was used by Druids as a 'power stone.' Feldspar is traditionally associated with creativity and detachment from the mundane.