Adularia
Feldspar
Published: June 2014
Modified: August 2021
Adularia is a variety of feldspar found in hydrothermal veins in mountainous areas, from one of which it derives its name: the Adular Mountains of Switzerland. It commonly forms as colorless to white, cream, pale yellow to pink, or reddish-brown, glassy, prismatic, twinned crystals. These transparent to colorless gems often display a white to blue sheen.
General Information
Common Name
Adularia
Species
Feldspar
Transparency
Transparent - Translucent
Dispersion
Strength: Weak Fire Value: 0.120
Refractive Index
1.518-1.536 Tolerance: (+0.010/-)0.010)
Birefringence
0.005- 0.010
Optic Character
Biaxial
Optic Sign
Negative
Polariscope Reaction
Doubly Refractive (DR)
Fluorescence
SWUV: Inert to weak orangy red
LWUV: Inert to weak blue or pink
LWUV: Inert to weak blue or pink
Pleochroism
Unobservable
Hardness
6
Streak
White
Specific Gravity
2.520-2.620 Typical:2.580
Inclusions
Adularia will display white or blue adularescence. Stones might have centipede like inclusions and material with aventuresence or asterism might contain reflective inclusions such as fine needles or elongated hematite platelets.
Luster
Vitreous
Fracture
Uneven, Splintery
Cleavage
Perfect, in two directions
Chemical Name
potassium aluminum silicate
Chemical Formula
KAlSi3O8
Crystal System
Monoclinic
Chemistry Classification
Silicate
Adularia Colors
-
Colorless -
Colorless -
Colorless
Countries of Origin
Austria; Pakistan; United States of America (the); Unknown; Sri Lanka; India
Care
Normal Care