Cacoxenite: Mineral Information


Cacoxenite is an iron aluminum phosphate mineral. It’s associated with iron ores.

It was first described in 1825 for an occurrence in the Hrbek Mine, Bohemia, Czech Republic. It occurs as a secondary phase in oxidized magnetite and limonite deposits. It also occurs in novaculites and in iron and phosphorus rich sediments.

Often times, it forms as fuzzy brownish yellow, brown, yellow, or gold radiated tufts or strands. It may also appear as reddish orange or greenish yellow. The cacoxenite is occasionally referred to cacoxene or cacoxitite.

Cacoxenite is a mineral that is commonly an inclusion in quartz, especially amethyst. The inclusions in amethyst often detract from the amethyst as the brown acicular needles dampen the pure purple color to a less desirable brownish hue. The inclusions of cacoxenite will certainly ruin any chance for the host stone to become a gemstone. This is not to say that some specimens of cacoxenite included quartz have no value, for indeed some are actually enhanced with interesting surreal landscaping effects.

Cacoxenite: Mineral Information
Radial Cacoxenite Crystals. La Paloma Mine, Zarza la Mayor, Mancomunidad Rivera de Fresnedosa, Cáceres, Extremadura, Spain. Photo: Rewitzer Christian.

Cacoxenite is associated with iron ores. The name comes from the Greek κăκός for "bad" or "evil" and ξένος for "guest" because the phosphorus content of cacoxenite lessens the quality of iron smelted from ore containing it.

Properties of Cacoxenite

Formula: Fe3+24Al(PO4)17O6(OH)12·17(H2O)
Color is yellow-brown, brown, reddish-yellow, greenish-yellow or yellow.
Luster is vitreous to silky.
Transparency: Specimens are translucent to transparent.
Crystal System is hexagonal.
Crystal Habits include acicular radiating crystals often as inclusions, also massive, globular, botryoidal and fibrous tufts.
Cleavage is poor.
Fracture is fibrous.
Hardness is 3 - 4
Specific Gravity is approximately 2.3 (below average).
Streak is yellow.
Associated Minerals include quartz, hematite, strengite, beraunite, rockbridgeite and limonite.
Notable Occurrences include Cornwall, England; Sweden; France; Hagendorf, Germany; Antwerp, New York; Pima County, Arizona; Indian Mountain, Alabama and Coon Creek Mine, Polk County, Arkansas, USA.
Best Field Indicators are crystal habit, color, associations, density and streak.
Occurrence: A common accessory mineral in oxidized magnetite and "limonite" iron ores; in Fe,Mn-bearing novaculites; a rare constituent of iron-rich sediments and soils.

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