Crystal Structure
Triclinic ordered analog of orthoclase.
Elemental Composition (by mass)
| Element | Mass % | Visual |
|---|---|---|
| O Oxygen | 45.99% | |
| Si Silicon | 30.27% | |
| K Potassium | 14.05% | |
| Al Aluminum | 9.69% |
Computed from simplified end-member formula. Solid-solution series, water content, and trace substitutions cause real-world variation.
IMA Abbreviation (Whitney-Evans 2010)
Mc
→ Microcline
K-feldspar low-T
Standard symbol from American Mineralogist (Whitney & Evans, 2010). Used in thin-section labeling, phase diagrams, and IMA-style species records.
Pronunciation
/ˈmaɪkroʊklaɪn/
↔ MY-kroh-cline
Greek "small angle"
Tenacity
Behavior:
brittle
Under stress:
Same
K-feldspar; includes amazonite.
Luster
vitreous
Bright greenish in amazonite.
Diaphaneity (Transparency)
translucent
Including amazonite.
Specific Gravity
2.54–2.57
g/cm³
light
K-feldspar; includes amazonite.
For comparison: water = 1.00, glass ≈ 2.5, quartz = 2.65, corundum ≈ 4.00, galena ≈ 7.50, gold ≈ 19.3.
Twinning Laws
Albite lawlamellar
Fine parallel striations on {001} — diagnostic for plagioclase but also appears in microcline.
Pericline lawlamellar
Cross-hatched grid pattern combined with albite-law twinning — diagnostic of microcline.
Cleavage & Fracture
Cleavage:
good 2 directions ~90°
Fracture:
uneven
Includes amazonite. Cleavage perpendicular.
Market availability: Common
Widely available in most dealer stocks. Specimens span all price tiers.
Collector tier: Solid Display
Reliable mid-tier display species. Easy to find in well-formed examples; broad locality diversity.
PolymorphsShares the formula
KAlSi3O8 with: Orthoclase · Sanidine — same chemistry, different crystal structure.Mohs 6–6.5
Vickers (~) 820 HV
Knoop (~) 870 HK
Nickel–Strunz
9.FA.30Dana
76.01.03.04Geological setting
Plutonic igneousPegmatiteMetamorphic
Element composition by mass
Formula: KAlSi₃O₈ · molar mass: 278.33 g/mol
| O | 45.99% | |
| Si | 30.27% | |
| K | 14.05% | |
| Al | 9.69% |
Computed from atomic weights (IUPAC 2021). Site-occupancy groups (Fe,Mn) split equally.
GroupFeldspar Group
Mohs Hardness
6–6.5
Microcline sits at 6–6.5 on the Mohs scale — just hard enough to scratch glass.
Colors:
Streak
White
White
Crystal system
Triclinic
Triclinic
Type localityPikes Peak, Colorado, USA
SilicatesSilicates (Tectosilicates — Feldspars)
TL;DR · 1 min read
Microcline (KAlSi₃O₈) is a triclinic potassium feldspar and the parent species of one of the most prized collector varieties — amazonite, the vivid blue-green form colored by trace lead and water content. Microcline forms in granitic pegmatites and high-grade metamorphic rocks; classic Pikes Peak (Colorado) and Madagascar deposits supply gem-grade amazonite.
Microcline (KAlSi₃O₈) is a triclinic potassium feldspar and the parent species of one of the most prized collector varieties — amazonite, the vivid blue-green form colored by trace lead and water content. Microcline forms in granitic pegmatites and high-grade metamorphic rocks; classic Pikes Peak (Colorado) and Madagascar deposits supply gem-grade amazonite.
More minerals to explore
Orthoclase (正长石)
Monoclinic
Labradorite (拉长石)
Triclinic
Sanidine (透长石)
Monoclinic
Albite (钠长石)
Triclinic
Varieties of Microcline
Microcline is a parent species — the following named varieties differ in color or chemistry but share the same fundamental mineralogy.
- Amazonite (u5929u6cb3u77f3)turquoise to blue-greenLead-bearing turquoise-green microcline variety, named for the Amazon River.