Lepidolite

Hand Specimen identification: Micaceous habit (see Figure 11), often a distinctive lilac-gray or rose color, and association usually serve to identify lepidolite.

Chemical Composition : K(Li,Al) 2 – 3(AlSi 3O10)(OH)2

Hardness : 2.5 to 4

Specific Gravity2.9

Cleavage/Fracture : perfect basal {001}/uneven

Luster/Transparency : pearly/translucent

Color : perfect basal {001}/uneven

Streak : white

Optical Properties : Lepidolite is generally colorless in thin section. It re-sembles muscovite but has lower relief and lower birefringence. Biaxial 1- 2, a = 1.53 to 1.55, b = 1.55 – 1.59, g = 1.55 to 1.59, d = 0.02 to 0.04, 2V = 0° to 60°.

Crystallography : Monoclinic, a = 5.21, b = 8.97, c = 20.16, b = 100.8°, Z = 4; space group C 2/m; point group 2/m.

Habit : Lepidolite usually forms coarse- to fine-grained scaly ag-gregates. It is less commonly disseminated as fine flakes.

Structure and composition : Lepidolite is actually a complex solid solution series with a structure similar to muscovite. Chemically, it is equiva-lent to muscovite with half or more of the octahedral Al replaced by Li, and perhaps Fe or Mg. In addition, other alkalis may substitute for K, and O or F may replace OH.

Occurrence and associations : Lepidolite is restricted to Li-rich pegmatites. Associated minerals include other Li minerals such as tourmaline, amblygonite, and spodumene, as well as the more common muscovite, feldspar, and quartz.

Varieties :

Related Minerals : Lepidolite has several polymorphs that cannot be differentiated without detailed X-ray study. It is iso-typical with other micas.