What is Rectorite?
Rectorite is a soft layered clay mineral and mixed-layer mica-smectite material, valued for pearly plates, unusual swelling behaviour and specialist locality specimens.
Mineralogy and crystal structure
Reference formula: (Na,Ca)Al4(Si,Al)8O20(OH)4·2H2O. Rectorite is compositionally and structurally variable, with ordered mica-smectite interlayers. No exact public COD model was selected, so the guide intentionally avoids a misleading single artificial lattice. Rectorite is classified with silicates and has a monoclinic crystal system. Typical hardness is 1.5–2 on the Mohs scale and specific gravity is approximately 2.2–2.6.
Colour, lustre and habit
Typical colours include white, cream, yellow, green, pink. The usual platy, micaceous, massive habit and pearly, earthy lustre help describe a specimen, but colour alone is not diagnostic.
Formation and notable localities
Rectorite forms in or is associated with hydrothermal alteration, weathered volcanic rocks and clay-rich low-temperature environments. Important documented localities include the United States, China, Japan, South Africa and other documented clay-mineral localities.
Layered clay chemistry in a soft collector mineral
Rectorite is a mineral for close observation rather than hardness or sparkle. Its commercial interest comes from the way layered structure, water and alteration history shape a soft pearly specimen.
Collecting and care
Keep dry and protected from abrasion; avoid soaking, heat and dusty preparation. Preserve the locality because visual identification is not sufficient.
