Hemimorphite
Hydrous zinc silicate (Zn4Si2O7(OH)2·H2O)
A hydrous zinc silicate, often sky-blue, that is an ore of zinc and a collectible mineral forming botryoidal crusts and crystals.
- Mohs hardness
- 4.5-5
- Color
- white, colorless, sky-blue to blue-green, brown
- Type
- mineral
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Overview
Hemimorphite is a hydrous zinc silicate (Zn4Si2O7(OH)2·H2O) named for its unusual hemimorphic crystals, which have differently shaped ends, a rare feature reflecting its polar crystal structure.
It occurs as colorless to white crystals, fan-shaped sprays, and, most famously, as botryoidal (grape-like) blue to blue-green crusts that are highly attractive. Historically it was lumped with smithsonite under the old name calamine.
Hemimorphite is both an ore of zinc and a popular ornamental and collector material, with the sky-blue botryoidal form being especially sought after.
Formation & geology
Hemimorphite is a secondary mineral that forms in the oxidized zones of zinc ore deposits, where primary zinc sulfide (sphalerite) is weathered and altered. The zinc recombines with silica and water to precipitate hemimorphite in cavities and along fractures.
It commonly occurs with smithsonite, sphalerite, galena, cerussite, and other oxidation-zone minerals, often as crusts, druses, and botryoidal masses.
Notable localities include Santa Eulalia and Mapimi in Mexico, the 79 Mine in Arizona, Tsumeb in Namibia, Sardinia in Italy, China (source of much blue ornamental material), and historic sites in Belgium and England.
How to identify it
Look for white to colorless platy crystals, fan-shaped sprays, or sky-blue to blue-green botryoidal crusts with a vitreous to silky luster. The blue botryoidal form is very characteristic.
Hemimorphite has a hardness of 4.5-5 and a white streak. It is pyroelectric and piezoelectric due to its polar structure. It does not effervesce in acid (distinguishing it from carbonates), though it may dissolve slowly.
Look-alikes include smithsonite (a carbonate, fizzes in acid, often heavier-feeling) and chrysocolla (softer). The hemimorphic crystals, blue botryoidal habit, and lack of acid effervescence help confirm hemimorphite.
Uses & significance
Hemimorphite is an ore of zinc, the metal used for galvanizing steel, in alloys such as brass, in die-casting, and in batteries. Historically, as part of calamine, it was vital to brass production and to the soothing calamine lotion of zinc compounds.
Today its attractive blue botryoidal material is popular for cabochons, beads, carvings, and collector specimens, valued for its color and patterns.
Metaphysically it is associated with calm and communication, though such claims are not scientific. Its main significance is as a zinc ore and as an ornamental and collectible mineral.
Frequently asked questions
What is hemimorphite used for?
It is an ore of zinc and is widely used as an ornamental stone for cabochons, beads, and carvings, especially the blue botryoidal variety.
Why is it called hemimorphite?
The name refers to its hemimorphic crystals, which have differently shaped terminations at each end due to its polar crystal structure.
How do I tell hemimorphite from smithsonite?
Smithsonite is a carbonate and effervesces in acid, while hemimorphite is a silicate and does not; hemimorphite also commonly forms platy crystals and sprays.
Is hemimorphite the same as calamine?
Historically calamine referred to both hemimorphite and smithsonite together; today the two are recognized as distinct minerals.
Where does blue hemimorphite come from?
Much of the blue botryoidal ornamental material comes from China, with fine specimens also from Mexico, Namibia, and Arizona.
Hemimorphite guides
In-depth guides for identifying, valuing, and understanding Hemimorphite.
Hemimorphite identified by the community
Real specimens identified with Rock Identifier.
