Anorthoclase
5 in the gallery
Anorthoclase is a feldspar mineral in which sodium and potassium can substitute within the same crystal structure, giving a solid solution across the Na-K feldspar series. It typically forms as slender, tabular to prismatic crystals and often exhibits a glassy to pearly luster. The color range is generally pale, from colorless to white or faint pink, and the mineral tends to occur in low-relief habits that reflect light softly rather than strongly. Crystals can be associated with granitic rocks and pegmatites, and they are sometimes found in skarn environments where late-stage magmatic processes leave behind alkali feldspars. Noted specimens are often characterized by clean faces and well-formed terminations that appeal to collectors seeking classic alkali feldspar aesthetics.
- Formula
- (Na,K)AlSi3O8
- Rarity
- Common
- Stability
- Stable
- Collector interest
- Moderate Interest
- Classification notes
- Tectosilicate, feldspar group
Key characteristics
- Crystal system
- triclinic
- Mohs hardness
- 6–6.5
- Specific gravity
- 2.57–2.6
- Luster
- vitreous, pearly
- Transparency
- transparent, translucent
- Color
- colorless, white, gray, yellow, pink
- Streak
- white
- Cleavage
- perfect
- Fracture
- uneven
- Crystal habit
- tabular, prismatic, granular, massive
- Gem mineral
Where Anorthoclase is found
Top localities
- Chihuahua1 specimen
About Anorthoclase
Collectors prize Anorthoclase for its historical role in alkali feldspar studies and for its straightforward, elegant crystal forms that complement other minerals in a cabinet display. Specimens from Japan and Mexico are among the more commonly cited sources, where the mineral occurs in diverse pegmatitic and contact-metamorphic settings. The mineral’s relative rarity in crisp, well-formed crystals compared with more abundant feldspars can enhance its appeal when such material is recovered with good luster and clarity. For mineral enthusiasts, Anorthoclase offers a clean, minimalistic look that pairs well with complementary minerals to emphasize its subtle brightness and form.