Potassium (K) Feldspar
Description: Potassium Feldspar, also called Orthoclase, also referred as “pink” feldspar, is found in many igneous granites and pegmatites, and metamorphic gneisses. It is the mineral assigned a hardness of "6" in the Moh's hardness scale.
Color: Colorless to white, greenish-white, grayish-yellow, and pale pink
Streak: White
Luster: Vitreous, Sub-Vitreous, Resinous
Fracture: Irregular, uneven, conchoidal
Cleavage: One perfect cleavage and one good cleavage intersecting at 90° (right angles)
Hardness: 6
Density/Specific Gravity: 2.55 - 2.63 g/cm3
Magnetism: N/A
Taste: N/A
Hydrochloric acid: N/A
Radioactivity: N/A
Fluorescence: N/A
Distinguishing Physical Properties:
Cleavage: Perfect, with cleavage faces intersecting at right angles
Lack of fine parallel striations that characterize the plagioclase minerals
Color: Potassium feldspars commonly have pink to reddish hues, while the plagioclase feldspars tend to be white or gray, but again, color is not a perfect diagnostic tool
Photograph Attribution: Potassium Feldspar specimen photograph by Sean C. Murphy, 2020.