What is Laumontite?
Laumontite is a delicate hydrated zeolite known for pale prismatic crystals, cavity growth and striking reactions to changes in humidity.
Mineralogy and crystal structure
Reference formula: CaAl2Si4O12·4H2O. Laumontite is a monoclinic zeolite with water in an open framework. Natural crystals may lose water and become powdery or opaque on drying, while the exact hydration state can vary; the selected COD model is therefore a representative hydrated structure. Laumontite is classified with silicates and has a monoclinic crystal system. Typical hardness is 3.5–4 on the Mohs scale and specific gravity is approximately 2.2–2.3.
Colour, lustre and habit
Typical colours include colourless, white, pink, yellow, grey. The usual prismatic, fibrous, radiating habit and vitreous, pearly lustre help describe a specimen, but colour alone is not diagnostic.
Formation and notable localities
Laumontite forms in or is associated with low-temperature hydrothermal veins, volcanic cavities and altered basaltic rocks. Important documented localities include India, Iceland, Japan, the United States, Canada and Scotland.
A fragile zeolite with sculptural form
Laumontite is prized for its elegant sprays and pale, architectural crystals. Its sensitivity is part of the story: the specimen visibly connects open-framework mineralogy with the water that helped create and preserve the cavity.
Collecting and care
Store dry but not overheated, avoid washing and handle gently because dehydration can weaken or alter crystals.
