Chalcanthite: Facts About Chalcanthite

Chalcanthite is a richly colored blue/green water-soluble sulfate mineral CuSO4·5H2O. It is commonly found in the late-stage oxidation zones of copper deposits. Due to its ready solubility, chalcanthite is more common in arid regions.

If a Chalcanthite crystal looks to good to be natural, it probably is, as good natural crystals are very hard to come across. Natural Chalcanthite crystals are very rare in nature.

Well-formed crystals are easily grown synthetically from copper sulfate solutions. This can be done by dissolving a readily available chemical salt called copper sulfate, and then letting the water evaporate.
Chalcanthite is a pentahydrate and the most common member of a group of similar hydrated sulfates, the chalcanthite group. These other sulfates are identical in chemical composition to chalcanthite, with the exception of replacement of the copper ion by either manganese as jokokuite, iron as siderotil, or magnesium as pentahydrite.

These are the members of the Chalcanthite Group:
  • Chalcanthite (Hydrated Copper Sulfate)
  • Jokokuite (Hydrated Manganese Sulfate)
  • Pentahydrite (Hydrated Magnesium Sulfate)
  • Siderotil (Hydrated Iron Sulfate)
Its blue crystals dehydrate to an opaque greenish-white powder on exposure to dry air.

Chalcanthite specimens must be kept away from water and moist conditions, since a chemical effect with water causes them to eventually crumble or dissolve.

Chalcanthite: Facts About Chalcanthite
Beautiful Chalcanthite from Planet Mine, La Paz Co., Arizona
Photo: @Allans_minerals/Instagram

There are many chemical uses for copper sulfate solutions. Copper sulfate solutions and crystals are a staple in well stocked chemistry labs. Metallic copper can be obtained from copper sulfate solutions by adding metallic iron, a process used in the mining and processing of chalcanthite. As a poison, copper sulfate solutions or crystals were used to clear ponds and waterways of plant growth, but this practice has stopped due to environmental concerns.

Identification of the mineral chalcanthite is generally pretty easy. Its bright blue color can be dulled on natural specimens, but it is otherwise very distinctive. Its solubility is also key if this test can be done with a small unnecessary fragment of the specimen in question. The resulting solution should turn blue. Another relatively common soluble sulfate is melanterite, FeSO4·7H2O, but it is generally greener.

Taste is a test that is used for some minerals such as halite and can be used on chalcanthite. Chalcanthite has a sweet metallic taste that is distinctive. However, it is not recommended as a test to be done casually for as was stated, chalcanthite is poisonous! If it is necessary, use a tip-of-the-tongue technique to minimize the risk.

In the U.S., the most prominent locality for Chalcanthite specimens is the Planet Mine, La Paz Co., Arizona. Other Arizona occurrences include Bisbee, Cochise Co.; Ajo and Tiger, Pinal Co.; Globe, Gila Co.; Morenci, Greenlee Co; and the Patagonia District, Santa Cruz Co. Also occurs in Bingham Canyon, Salt Lake Co., Utah; and Ducktown, Polk Co., Tennessee.

Note of caution: Chalcanthite is poisonous and should not be taste-tested, unless the lick is minor and it is spit out and rinsed immediately.


Color is a bright and deep blue.
Luster is vitreous.
Transparency: Crystals are transparent to translucent.
Crystal System is triclinic; bar 1.
Crystal Habits include rare, individual, natural crystals showing well formed slanted prismatic, tabular or lense-shaped forms, more commonly aggregated into columnar, curved, parallel growth structures. Also found as encrusting, stalactitic and granular masses and as vein filling deposits.
Cleavage is poor (basal).
Fracture is conchoidal.
Hardness is 2.5
Specific Gravity is approximately 2.2 - 2.3 (noticeably below average).
Streak is pale blue to colorless.
Other Characteristics: Is very soluble in water. A fact that is a detriment to most collection specimens as they may absorb water from the air and deteriorate over time. The taste has a sweet metallic character, but do not do this test often or with more than just a tip-of-the-tongue technique and only if needed to confirm an identification as chalcanthite is poisonous!
Associated Minerals are brochantite, calcite , melanterite, aragonite, malachite and chalcopyrite.
Best Field Indicators are crystal habit, low density, associations, solubility in water, taste and color.

See also:
Crystal Habits and Forms
Chrysanthemum Stone: Natural Flower Stone
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