Monoclinic
2/m (C2h)
Three unequal axes, two at 90 degrees, one inclined (a ≠ b ≠ c, alpha = gamma = 90, beta ≠ 90)
The monoclinic crystal system has three axes of unequal length with one axis inclined to the other two. It is the most common crystal system for minerals. Crystals typically form prismatic or tabular habits. Includes orthoclase, clinopyroxene, gypsum, epidote, and many amphiboles.
The monoclinic crystal system is the most common crystal system for minerals, hosting approximately 32% of all known species. Its three unequal axes include one oblique angle (a ≠ b ≠ c, α = γ = 90°, β ≠ 90°), creating a characteristic 'leaning' appearance. The slight departure from perpendicularity gives monoclinic crystals their distinctive tilted geometry, readily visible in minerals like orthoclase feldspar and gypsum.
Symmetry
Monoclinic symmetry requires one two-fold rotation axis (the b-axis) and/or one mirror plane perpendicular to it. The oblique β angle (typically 90-120°) breaks the rectangular symmetry of the orthorhombic system. The system contains 3 crystal classes: prismatic (most common, with 2/m symmetry), sphenoidal, and domatic. The characteristic 'clinopinacoid' face ({010}) is perpendicular to the unique b-axis. Twinning is extremely common in monoclinic minerals, with contact twins (like gypsum's 'swallowtail' twins) and penetration twins (like orthoclase's Carlsbad twins) being classic examples.
Bedeutende Mineralien
The feldspars — the most abundant mineral group in Earth's crust — include monoclinic members like orthoclase and sanidine (potassium feldspars). Gypsum (CaSO₄·2H₂O) forms transparent 'selenite' crystals up to 12 meters long in Mexico's Cave of the Crystals. Augite and hornblende, the most common pyroxene and amphibole respectively, are monoclinic and abundant in igneous and metamorphic rocks. Epidote forms distinctive pistachio-green prismatic crystals. Malachite's rich green color and banded patterns make it one of the most recognizable monoclinic minerals, prized for ornamental use since ancient Egypt.
Minerale (10)
Gypsum
CaSO4 · 2H2O
07 Sulfates, Chromates, Molybdates, and Tungstates
Talc
Mg3Si4O10(OH)2
09 Silicates
Muscovite
KAl2(AlSi3O10)(OH)2
09 Silicates
Biotite
K(Mg,Fe)3(AlSi3O10)(OH)2
09 Silicates
Malachite
Cu2(CO3)(OH)2
05 Carbonates and Nitrates
Azurite
Cu3(CO3)2(OH)2
05 Carbonates and Nitrates
Wolframite
(Fe,Mn)WO4
07 Sulfates, Chromates, Molybdates, and Tungstates
Staurolite
Fe2Al9Si4O23(OH)
09 Silicates
Epidote
Ca2(Al,Fe)3(SiO4)(Si2O7)O(OH)
09 Silicates
Feldspar (Orthoclase)
KAlSi3O8
09 Silicates