Kidwellite Locality: Three Oaks Gap workings (Arena 1 prospect), Three Oaks Gap, Polk County, Arkansas , USA ( Locality at mindat.org ) Size: 4.0 x 3.3 x 2.9 cm. An exceptional specimen of this rare phosphate species with rich botryoidal growths on a display-quality matrix. It is from the noted collection of Arkansasan Clyde Hardin. — Photo: Robert M. Lavinsky · CC BY-SA 3.0
Kidwellite
An uncommon iron phosphate discovered in Arkansas, named in 1978 for Albert Lewis Kidwell.
Intro adapted from Wikipedia (CC BY-SA).
Kidwellite is an IMA-recognized mineral species in the phosphate class, with the chemical formula NaFe³⁺₉₊ₓ(PO₄)₆(OH)₁₁·3H₂O (x ≈ 0.33).
It crystallizes in the monoclinic crystal system (space group P2/c).
Key properties: Mohs hardness 3; specific gravity 3.3; Yellow streak; Silky luster; optically biaxial.
IMA symbol Kdw, IMA status: approved, named in 1974.
Found as a late-stage replacement of earlier phosphate minerals.
It is found associated with Rockbridgeite, beraunite, strengite, dufrénite, chalcosiderite, goethite.
The mineral was named to honor Albert Laws Kidwell (1919-2008), Houston, Texas, USA, for his study of Arkansas phosphate deposits.