• Chemistry: NaFe9(PO4)6(OH)10 - 5H2O, Hydrated Sodium Iron Phosphate Hydroxide.
  • Class: Phosphates
  • Uses: Only as mineral specimens.
  • Specimens

Kidwellite is a rare, typically yellow-green phosphate mineral. Its color is distinctive as well as its compact encrusting crystal habit. It is found in phosphate deposits with other rare phosphates from classic localities such as Cornwall, England.


  • Color is yellow-green, pale green or yellow.
  • Luster is vitreous.
  • Transparency: Specimens are translucent to transparent.
  • Crystal System is monoclinic; 2/m
  • Crystal Habits include compact encrusting aggregates, also massive and fibrous.
  • Cleavage is poor.
  • Fracture is fibrous.
  • Hardness is 3 - 4
  • Specific Gravity is approximately 2.5 - 3.4 (average to slightly above average).
  • Streak is green.
  • Associated Minerals include strengite, beraunite, dufrenite, rockbridgeite and limonite.
  • Notable Occurrences include Cornwall, England and Coon Creek Mine, Polk County, Arkansas, USA.
  • Best Field Indicators are crystal habit, color, associations and streak.
KIDWELLITE specimens:
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KIDWELLITE specimen kid-1
$ 75.00
Dims: 3.4 x 2.2 x 2.1" (8.5 x 5.7 x 5.4 cm)
Wt: 9.7 oz. (274 g)
Three Oaks Gap Mine, Coon Creek, Polk County, Arkansas, U.S.A.
A few rounded Kidwellite nodules rest on the pale base rock of this cabinet specimen. Most of these nodules are either broken or naturally incomplete, but one is intact and in excellent condition. The largest measures 0.6" (1.5 cm) in diameter and is broken open, revealing its compact, radial structure. All have a color that ranges from pale to deep green and all show a dull silky luster. A sizeable amount of rusty material (likely limonite) is present in and around the nodules.
no photo
kid-1 ($ 75.00)
Three Oaks Gap Mine, Coon Creek, Polk County, Arkansas, U.S.A.
KIDWELLITE specimen kid-2
$ 50.00
Dims: 3.6 x 2.8 x 1.3" (9.1 x 7.1 x 3.4 cm)
Wt: 8.1 oz. (230 g)
Three Oaks Mine, Coon Creek, Polk County, Arkansas, U.S.A.
A cluster of round Kidwellite nodules rests on one side of this cabinet specimen. These clusters reach diameters of 0.5" (1.3 cm) or more, but all of them are broken and incomplete. This breakage allows one to see the compact, acicular and radiating habits of their crystals, which are too fine and tightly arranged for effective study. All have a dull brown-green color and a dull silky luster. Some of these clusters contain limonite in their cores. All rest on a base of botryoidal hematite.
no photo
kid-2 ($ 50.00)
Three Oaks Mine, Coon Creek, Polk County, Arkansas, U.S.A.
KIDWELLITE specimen kid-3
$ 30.00
Dims: 2.80x2.47x2.25in (7.12x6.27x5.73cm)
Wt: 9.56oz (271g)
Coon Creek, Polk County, Arkansas, USA
One side of this specimenhas an exposed cavity lined with a crust of pale green kidwellite. A loupe reveals that the kidwellite is in tiny botryoidal masses showing no hint of crystal form, even along the broken edges. However, tiny patches of rockbridgite are visible along some edges. The back of the specimen is also interesting, showing a dozen broken radial clusters of duffrenite, with several other minerals also present including more kidwellite.
no photo
kid-3 ($ 30.00)
Coon Creek, Polk County, Arkansas, USA


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