Feldspar (Albite/Oligoclase)
Feldspar var. Albite/Oligoclase · Mineral Specimen / Rock-forming Mineral
Crystal System
Triclinic; typically occurs in massive, granular, or tabular habits with characteristic polysynthetic twinning visible as fine striations on cleavage planes.
Mineral Group
Silicates; Tectosilicate (Framework Silicate); Feldspar Group (Plagioclase series)
Chemical Formula
(Na,Ca)Al(Si,Al)3O8 (Sodium Calcium Aluminum Silicate)
Formation Process
Primarily Igneous (crystallizing from cooling magma) but also found in Metamorphic rocks through regional or contact metamorphism.
About This Crystal
The specimen shows a white to off-white coloration with a pearly to vitreous luster. It exhibits a blocky, crystalline structure with distinct cleavage surfaces. The transparency ranges from translucent to opaque, with visible internal fractures and a somewhat grainy surface texture integrated with a darker matrix.
Physical Characteristics
Color: White/Cream; Streak: White; Cleavage: Perfect in two directions at nearly 90 degrees; Fracture: Uneven to conchoidal; Specific Gravity: 2.60–2.65; Fluorescence: Occasionally weak reddish or white under UV.
Optical Properties
Refractive Index: 1.52–1.55; Birefringence: Weak; Pleochroism: Absent; Optical Phenomena: May show adularescence or labradorescence (schiller effect) in high-quality specimens.
Hardness & Durability
Origin Region
Globally abundant; notable localities include Norway, Canada, and the United States. Frequently found in granitic pegmatites and metamorphic rocks.
Hardness & Durability
Mohs Hardness: 6.0–6.5; Toughness: Brittle; Stability: Generally stable but susceptible to weathering into clay minerals over long periods.
Care & Maintenance
Clean with warm soapy water and a soft brush; avoid ultrasonic cleaners if internal fractures are present. Store separately from harder minerals like quartz to prevent scratching.
Rarity & Value
Common; very low value for raw rock-forming specimens. Value increases significantly for varieties showing optical effects like Sunstone or Moonstone.
Special Characteristics
Often exhibits 'twinning striations'—tiny parallel grooves on the cleavage face that distinguish plagioclase from orthoclase feldspar.
Lore & History
Historically used as a foundational stone in architecture and glass-making. In metaphysical lore, it is believed to assist in finding unconventional paths to goals and enhancing creativity.