What is Liddicoatite?
Liddicoatite is a lithium- and calcium-rich tourmaline species known for vivid zoning, strong pleochroism and exceptional pegmatite crystals.
Mineralogy and crystal structure
Reference formula: Ca(Li2Al)Al6(BO3)3Si6O18(OH)4. Liddicoatite is a trigonal tourmaline-group species with complex cation ordering and frequent colour zoning. Natural compositions vary, so the selected COD structure is a representative natural liddicoatite analysis rather than a universal formula for every specimen. Liddicoatite is classified with silicates and has a trigonal crystal system. Typical hardness is 7–7.5 on the Mohs scale and specific gravity is approximately 3.0–3.2.
Colour, lustre and habit
Typical colours include red, pink, green, brown, blue. The usual prismatic, columnar, striated habit and vitreous lustre help describe a specimen, but colour alone is not diagnostic.
Formation and notable localities
Liddicoatite forms in or is associated with lithium-rich granitic pegmatites and late-stage boron-rich cavities. Important documented localities include Madagascar, Brazil, Afghanistan, Mozambique, the United States and Namibia.
Tourmaline colour zoning at its most expressive
Liddicoatite is built for close viewing. A single prism can move from red to green, pink or brown as the eye follows its zoning, turning a complex pegmatite chemistry into a highly desirable natural colour composition.
Collecting and care
Hard but brittle along fractures; protect terminations, avoid sudden thermal shock and disclose treatments or cutting orientation in gem material.
