How to identify Pink Feldspar

To correctly identify Pink Feldspar (Potassium Feldspar (Orthoclase or Microcline)), check each of these features in order. Many rocks and minerals look alike, so cross-reference multiple properties before deciding.

Step-by-step identification

1. 1

   Color

   Overall color and any zoning or banding

   Typically pink, salmon-pink, reddish-pink, or flesh-colored. Can also be white, gray, or yellowish, but the 'pink feldspar' designation specifically refers to the pink varieties.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Vitreous (glassy) to pearly on cleavage surfaces.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Often forms anhedral to subhedral grains in igneous and metamorphic rocks. Can form euhedral crystals in pegmatites or vugs. Microcline may exhibit characteristic 'grid twinning' visible under a petrographic microscope.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Monoclinic (Orthoclase, Sanidine) or Triclinic (Microcline). Crystals are typically prismatic, often with Carlsbad twinning, Baveno twinning, or Manebach twinning. In granitic rocks, it often forms blocky, anhedral to subhedral grains.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Two perfect cleavages intersecting at approximately 90 degrees (90° for orthoclase, 89°30' for microcline). This is a key diagnostic feature.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Common in felsic igneous rocks (granite, granodiorite, syenite, rhyolite), pegmatites, and high-grade metamorphic rocks (gneiss, schist). Also found as detrital grains in arkosic sandstones.

Key Facts

Hardness

6 on the Mohs scale

Specific Gravity

2.55 - 2.63 g/cm³

Crystal System

Monoclinic (Orthoclase, Sanidine) or Triclinic (Microcline)

Color

Pink, salmon-pink, reddish-pink, white, gray, yellowish

Luster

Vitreous to pearly

Transparency

Transparent to translucent

Fracture

Uneven to conchoidal

Cleavage

Two perfect cleavages at approximately 90 degrees

Composition

Potassium aluminum silicate (KAlSi3O8)

Physical characteristics

• Crystal Habit: Prismatic, blocky, anhedral to subhedral grains; often twinned (Carlsbad, Baveno, Manebach)
• Cleavage Type: Perfect on {001} and {010}
• Fracture Type: Uneven to conchoidal
• Tenacity: Brittle
• Luster Type: Vitreous to pearly

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