Quartz , Rectorite Locality: Jeffrey Quarry, Jeffrey , Pulaski County, Arkansas , USA ( Locality at mindat.org ) Size: miniature, 4.5 x 4.2 x 4 cm Rectorite w/Quartz Interesting specimen of "mountain leather", a decrepitated claylike mineral that has the feel and sturdiness of cardboard. — Photo: Robert M. Lavinsky · CC BY-SA 3.0
Rectorite
Rectorite is an IMA-recognized mineral species in the silicate class, with the chemical formula (Na,Ca)Al₄(Si,Al)₈O₂₀(OH)₄·2H₂O.
It is a member of the Corrensite, Clay structural group.
Key properties: Mohs hardness 1; specific gravity 2.34; Pearly to greasy when massive luster.
IMA symbol Rec, IMA status: approved, named in 1891.
Found in some low-temperature hydrothermal argillic alteration zones, along veins and pervasively replacing potassic feldspar. In altered bentonites; may develop from muscovite during diagenesis of shales.
It is found associated with Quartz, cookeite, ankerite, apatite, pyrite, sphalerite, galena, rutile (Jeffrey quarry, Arkansas, USA).
The name refers to E.W. Rector (1849–1917), lawyer of Hot Springs, Arkansas, USA.