Cacoxenite is highly prized by collectors for its stunning, radiating sprays of golden-yellow needles that often look like tiny sunbursts. It is most frequently found as an inclusion within quartz crystals, known as super seven or amethyst cacoxenite, where the delicate plumes are preserved within the clear host. It typically forms in the oxidized zones of iron-rich mineral deposits.
Is this cacoxenite?
5-step field checkRun through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.
- 1Test the hardnessTry to scratch cacoxenite with a known reference. Cacoxenite sits at Mohs 3-4, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: yellow.
- 3Read the lusterHold the specimen under a strong light. Luster: silky.
- 4Match the color rangeCompare against the expected color range: yellow, brownish yellow, green, golden yellow, red yellow.
- 5Look at form & habitCrystal system: hexagonal. Typical habit: acicular, radial, stellate.
Often confused with
Cacoxenite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Goethite is the harder of the two (Mohs 5-5.5 vs. 3-4); streak differs, so Cacoxenite leaves yellow, Goethite leaves brownish yellow, yellow-orange, ocher-yellow; luster reads silky on Cacoxenite and imperfect adamantine metallic to dull earthy; silky when fibrous on Goethite.
How to tell apart: Streak differs, so Cacoxenite leaves yellow, Wavellite leaves white; luster reads silky on Cacoxenite and vitreous to resinous, pearly on Wavellite.
Often found alongside cacoxenite
Minerals reported to co-occur with cacoxenite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Fe₂₄AlO₆(PO₄)₁₇(OH)₁₂·75H₂O
- Mohs hardness
- 3-4
- Density
- 2.2-2.6 g/cm³
- Colors
- Streak
- Yellow
- Luster
- Silky
- Transparency
- Semitransparent
- Crystal system
- Hexagonal
- Crystal habit
- Acicular, radial, stellate
- Cleavage
- None
- Rarity
- Uncommon
- Uses
- Collector, Study mineral
- Host rock
- 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
Where rockhounds find cacoxenite
Classic worldwide localities
- Palermo #1 mine, near North Groton, Grafton Co., New Hampshire, USA
- Hellertown, Northampton Co., Moore's Mill, Cumberland Co., and Noble's mine, Lancaster Co., Pennsylvania, USA
- Indian Mountain, Cherokee Co., Alabama, groups large for the species, USA
- Wilson Springs (Potash Sulphur Springs) mine, Garland Co., from the Avant claim, about three km southwest of Shady, and at Three Oak Gap, Polk Co., Arkansas, USA
- Hrbek mine, Svata Dobrotiva (St. Benigna), Czech Republic
- Tfenice, Czech Republic
Field-hunting tip
Where it forms: 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. If you start seeing dufrenite, rockbridgeite, beraunite in float, you are in the right ground. Typical habit: acicular, radial, stellate. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify cacoxenite?+
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What rocks look like cacoxenite?+
What minerals are found with cacoxenite?+
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Find cacoxenite on the map
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