Nacrite Locality: „Frohe Hoffnung“-shaft, Wildental, ore mountains Exposed in the Mineralogical Museum of University Bonn, Germany — Photo: Ra'ike · CC BY-SA 3.0
Nacrite
A kaolinite polymorph stacking its layers differently — distinguishable only by X-ray diffraction.
Intro adapted from Wikipedia (CC BY-SA).
Nacrite is an IMA-recognized mineral species in the silicate class, with the chemical formula Al₂Si₂O₅(OH)₄.
It crystallizes in the monoclinic crystal system (space group Cc). It is a member of the Clay, Kaolinite structural group.
Key properties: Mohs hardness 2–2.5; specific gravity 2.5–2.7; Pearly luster; optically biaxial.
IMA symbol Ncr, grandfathered status — known before the IMA’s founding, named in 1807.
Hydrothermal in origin.
It is found associated with Kaolinite, dickite, mica, quartz.
The name comes from the French nacre, for mother of pearl, in allusion to its appearance.