What is Chalcedony?
Chalcedony is a durable microcrystalline silica aggregate, valued for smooth waxy surfaces, translucent colour and the natural patterns that make each cutting piece different.
Mineralogy and structure
Reference formula: SiO2. Chalcedony is a silica-rich material and aggregate of very fine quartz and moganite. Chalcedony is not a separate crystal lattice like quartz: it is a microcrystalline to cryptocrystalline aggregate, commonly containing quartz and moganite. The SiO2 composition is useful reference chemistry, but no single unit cell should be presented for the whole material. The reference record uses no single crystal system applies to the aggregate symmetry. Typical hardness is 6.5–7 on the Mohs scale and specific gravity is approximately 2.58–2.64.
Colour, lustre and habit
Typical colours include white, grey, blue, pink, brown, orange, green. The usual botryoidal, massive, fibrous habit and waxy, vitreous, dull lustre help describe a specimen, but colour alone is not diagnostic.
Formation and notable localities
Chalcedony forms in or is associated with silica-rich fluids filling cavities, fractures and vesicles in volcanic rocks, followed by slow deposition and replacement. Important documented localities include Brazil, Uruguay, India, Madagascar, Namibia, Turkey and the United States.
Why it sells
Chalcedony is a strong decorative material because its colour and translucency survive polishing while its internal banding, moss-like inclusions and cavity textures keep every cabochon visually individual.
Collecting and care
Chalcedony is relatively durable, but avoid hard knocks on thin cabochons and prolonged exposure to strong acids or aggressive heat. Keep untreated colour and any dyeing or stabilisation clearly documented.
