Formula: NaFe³⁺_9+x(PO₄)₆(OH)₁₁ · 3H₂O, x = 0.33

Species:

Colour: Greenish yellow, Greenish white, Yellow, Light green

Lustre: Resinous, Waxy, Silky, Dull

Hardness: 3

Specific Gravity: 3.04 – 3.3

Crystal System: Monoclinic

Name: Named by Paul (Paulus) B. Moore and Jum Ito in 1978 in honor of Albert Lewis (or Laws) Kidwell (1919 – 2008), mineral collector and research geologist with Carter Oil Company and later Exxon Oil Company, Houston, Texas, USA.

Type Locality: Fodderstack Mountain, Norman, Montgomery County, Arkansas – USA

Occurs as replacement of rockbridgeite and beraunite. Dufrénite or natrodufrénite may overgrow, in an epitaxial way, kidwellite, and vice-versa. May be confused with meurigite-Na.