Gem library
Hemimorphite
Zinc silicate in blue draperies
Hemimorphite forms turquoise-blue crusts in draperies and clusters that line the cavities of old zinc mines. Its name states a crystallographic oddity: its crystals do not have matching ends, and that gives them an electrical property.
- Hardness (Mohs)
- 4.5 – 5
- Density
- 3.40 – 3.50
- Crystal system
- Orthorhombic
- Refractive index
- 1.614 – 1.636
- Cleavage
- Perfect on {110}
Mineralogical identity
- Family
- Silicates, sorosilicates
- Species
- Hemimorphite
- Variety
- Blue botryoidal hemimorphite
- Chemical formula
- Zn₄Si₂O₇(OH)₂·H₂O
- Crystal system
- Orthorhombic
- Classification
- Collector's mineral · ornamental stone
- Rarity
- Uncommon
- Indicative price
- €1 – 25/ct
Etymology
From the Greek hemi, «half», and morphê, «form»: the crystals are hemimorphic, that is, different at each of their two ends, which is rare.
Physical & optical properties
- Hardness (Mohs)
- 4.5 – 5
- Density
- 3.40 – 3.50
- Refractive index
- 1.614 – 1.636
- Birefringence
- 0.022
- Cleavage
- Perfect on {110}
- Fracture
- Conchoidal
- Lustre
- Vitreous to silky
- Diaphaneity
- Translucent to opaque
- UV fluorescence
- Weak
- Pleochroism
- Weak
- Colours
- blue, turquoise blue, white, green, colourless
Formation, geology & history
A mineral of the iron cap
Hemimorphite is a secondary mineral: it does not exist in the primary deposit, it appears there when water and air attack the zinc sulphides. In the oxidation zone of zinc mines, sphalerite dissolves and the zinc migrates to precipitate lower down, as a carbonate (smithsonite) or a silicate (hemimorphite) depending on the silica available. It is therefore always found in that altered zone miners call the iron cap. Eighteenth-century mineralogists confused the two under the name calamine; it was James Smithson, founder of the Smithsonian Institution, who demonstrated in 1803 that these were two distinct species.
Hemimorphy and piezoelectricity
Almost all crystals have two identical ends. Hemimorphite is the exception: one end is pyramidal, the other flat, because its internal structure has no centre of symmetry. That asymmetry has a direct physical consequence: compressed, the stone develops a difference of electrical potential between its two ends. That is piezoelectricity, the same property that makes a quartz gas lighter work. Heated, it polarises too: that is pyroelectricity. These properties never found a practical use for this mineral, too rare in usable crystals, but they make it a textbook case.
The blue, and what is made of it
The turquoise blue comes from traces of copper, and it is present only in certain deposits, notably in Yunnan. The material reaches the market as plates carpeted with small bright spheres, barely polished so as not to destroy the botryoidal texture. The transparent crystals, colourless or pale blue, from Mapimí in Mexico, are facetable collector's pieces but very delicate: hardness 5 and perfect cleavage. The blue colour is not stable in sunlight, and exposed pieces gradually lose their intensity.
How to recognise it
- Spheres side by sideThe botryoidal form, in tight, glossy grape-like clusters, is very characteristic. Chrysocolla, of a neighbouring tint, forms smooth or earthy crusts instead.
- Density3.45: for so soft a mineral, that is heavy. Compared with a chrysocolla (2.2) of the same volume, the difference is felt in the hand.
- FluorescenceUnder UV, some pieces give a weak, whitish to greenish response. It is not systematic, but it is a clue in the mineral's favour.
Imitations, treatments & confusions
- Chrysocolla and turquoise sold as hemimorphiteAll three are blue copper minerals, and the confusion is common. Density and the clustered form settle it.
- Dyed resin on a support«Hemimorphite» plates that are aggregates of bound powder. Too regular a surface, identical spheres, and a bead of water that sits instead of soaking in.
- Blue smithsoniteA true neighbour, same deposit, sometimes the same look. It fizzes in acid, hemimorphite does not: the test is decisive.
Deposits & origins
China (Yunnan, the blue draperies of the trade), Mexico (Mapimí, Durango), Namibia (Tsumeb), United States (New Mexico), Italy (Sardinia), Greece, Iran
Care & precautions
- No water: the perfect cleavage and the porous structure of the clusters hold moisture and dull the stone.
- Away from sunlight, which fades the blue irreversibly.
- Never ultrasonics: the spheres come away from their support.
- Store on a flat support, the draperies break under their own weight if laid askew.
Traditions & crystal healing
- Chakras
- Throat · heart
- Zodiac signs
- Libra · Gemini
- Element
- Air
It is presented as a stone of sincere speech and responsibility, often recommended in handbooks for situations where one has to own up rather than run. Cultural heritage, never medicine.
The virtues described here belong to tradition and cultural heritage. They are in no way medical advice and never replace a consultation.
Frequently asked questions
Hemimorphite or chrysocolla?
Density settles it: 3.45 against 2.2. In the hand, hemimorphite is distinctly heavier. Its form in small bright spheres is also more regular than chrysocolla's crusts.
Can it be set in jewellery?
In a protected pendant, yes. Not in a ring: hardness 5 and perfect cleavage do not stand up to daily use.
Why is it so blue only in some places?
Copper. It is present only in deposits where zinc and copper weather together, as at Yunnan or Tsumeb. Elsewhere, hemimorphite is white or colourless.
Tools for this stone
Hemimorphite: only the tools this stone actually concerns, each carrying the value read on this page.