Lepidolite

Lepidolite belongs to the group of lithium-bearing micas and is one of the most important minerals for lithium extraction worldwide. Its structural formula reveals a complex superposition of layers of silicon-aluminum tetrahedra and lithium-aluminum octahedra, bonded together by potassium ions. This atomic arrangement explains the characteristic perfect cleavage along the (001) plane, which enables separation into very thin and slightly flexible sheets. Color ranges from pale pink to violet, white, and yellow, often with the vitreous-pearlescent luster typical of micas.

It forms predominantly in lithium-rich granitic pegmatites, often in association with other lithium-bearing minerals such as spodumene, petalite, and tourmaline. Pegmatites are igneous rocks with very coarse grain size that crystallize slowly from magmas rich in incompatible elements. Lepidolite represents a late crystallization stage, when lithium becomes concentrated in residual fluids. From a gemological perspective, lepidolite is not used in jewelry, but its economic value lies in its lithium content: a single ton of ore can contain 1–2% Li₂O. Significant deposits are found in Australia (Greenbushes), Brazil, Czech Republic, and Zimbabwe, with global production dominated by large-scale operations dedicated to lithium extraction for lithium-ion batteries.

Crystal system: Monoclinic, space group C2/m. Typical lattice parameters: a ≈ 5.3 Å, b ≈ 9.2 Å, c ≈ 10.3 Å, β ≈ 100.8°. Hardness: 2.5–3 Mohs. Density: 2.8–3.0 g/cm³ (varies with lithium and iron content). Perfect cleavage along (001), characteristic of micas. Refractive index: nα ≈ 1.525, nγ ≈ 1.548 (birefringence ≈ 0.023). Pleochroism: weak to moderate, with chromatic variations depending on orientation. IR Spectroscopy: characteristic O-H stretching bands around 3600–3700 cm⁻¹ and Si-O-Si absorptions in the 900–1200 cm⁻¹ region. Chemical analysis: Li₂O content ranges from 3.5% to 8% by weight; K₂O content is typically 8–10%. Composition may include traces of Rb, Cs, Fe, and Mn. UV Fluorescence: generally inert, although some specimens may exhibit weak red fluorescence under 254 nm UV. Common mineral associations: spodumene, petalite, alkali feldspar, quartz, lithium-bearing tourmaline, beryl. Geological setting: zonal pegmatites of LCT type (Lithium-Cesium-Tantalum), often in the intermediate to distal zone of pegmatites.