THE MINERAL HEMIMORPHITE


Hemimorphite is one of the more common sorosilicates. Its most noteworthy characteristic is its polar or hemimorphic crystals from where it gets its name. The crystal structure produces a different termination at each end of the crystal. One termination, the "bottom" is rather blunt being dominated by a pedion face while the opposite end, the "top" is terminated by the point of a pyramid. The crystal structure contains tetrahedrons of ZnO3 OH, interlocked with Si2 O7 groups and water molecules. The zinc is at the center of the tetrahedron while the three oxygens, along with an OH group, are at the four points of the tetrahedron. These tetrahedrons are all aligned in the same direction with one face parallel to the pedion termination and the "top" of the tetrahedrons pointing toward the pyramidal termination.

Hemimorphite was originally named calamine but this name had been used for another mineral and hemimorphite was proposed and is now in wide spread use. The hemi means half while the morph means shape and thus hemimorphite is aptly named. Only a few other minerals show hemimorphic character such as tourmaline, but none show it as well as hemimorphite. Clusters of hemimorphite that show well shaped crystals do not always show the hemimorphic character. Because the crystals of a single specimen tend to grow outward with either the "top" or the "bottom" as the overall orientation for that specimen. In order to see the hemimorphic character either a doubly terminated specimen is necessary or two different clusters with different orientations will be needed.

Specimens of hemimorphite tend to be of two very different forms (seems like a trend with this mineral). One form produces very glassy, clear or white, thin, bladed crystals, often well formed showing many crystal faces. Many times these crystals are arranged in fan shaped aggregates. The other form produces a blue to blue-green botryoidal crust that resembles smithsonite or prehnite. Prehnite has a lower density and is usually greener and has different associations with other minerals. Smithsonite has a shimering luster that causes a play of light across the rounded surfaces and has a higher density that hemimorphite. Often hemimorphite will show rough crystal ridges or "cock's comb" structures over top of the basic botryoidal crust. For a collector both forms are a must in their mineral collections.

PHYSICAL CHARACTERISTICS:

  • Color is blue-green, green, white, colorless, brown and yellow.
  • Luster is vitreous in large crystals to dull in more compact forms.
  • Transparency crystals are transparent to translucent.
  • Crystal System is orthorhombic; mm2
  • Crystal Habits include the bladed crystal form and the botryoidal form as the most common. The crystals are usually elongated and flat. The terminations are different at each end. One termination is blunted by a pedion face that is usually bevelled by several dome faces. The other end is pointed, being capped by a pyramid. The other common form is botryoidal producing a grape bunch texture. Often the botryoidal form has a cock's comb appearance showing rough crystal terminations.
  • Cleavage is perfect in one direction.
  • Fracture is conchoidal to subconchoidal.
  • Hardness is slightly less than 5.
  • Specific Gravity is approximately 3.4+ (above average)
  • Streak is white.
  • Associated Minerals include limonite, aurichalcite, calcite and smithsonite.
  • Other Characteristics: strongly pyroelectric and piezoelectric.
  • Notable Occurrences include Santa Eulalia and Mapimi, Mexico; New Mexico and New Jersey, USA: England and Zambia.
  • Best Field Indicators are crystal habit, color, density and luster.
This Site Awarded
Available HEMIMORPHITE specimens:
HEMIMORPHITE specimen HMI-18
$ 39.00 -20% = $ 31.20
Dims: 2.32x0.96x1.01in (5.90x2.43x2.57cm) .... Wt: 1.20oz (34.0g) .... Loc: Level 16, Mina El Potosi, Santa Eulalia, Chihuahua, Mexico
This is a beautiful hemimorphite specimen, with originally white crystals overlain with a layer of amber-colored hemimorphite, showing an excellent adamantine luster, all covered with a light dusting of tiny reddish-brown and/or gray crystals, possibly limonite and/or goethite.
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HMI-18
$ 31.20
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HEMIMORPHITE specimen HMI-19
$ 30.00 -20% = $ 24.00
Dims: 2.40x1.56x1.28in (6.09x3.95x3.24cm) .... Wt: 4.0oz (114g) .... Loc: Level 8, San Antonio El Grande Mine, Chihuahua, Mexico
The host rock of this specimen is covered with a thick druze of hemimorphite which appears gray but a loupe shows that the individual crystals are colorless but tinted by very fine crystals of hematite. While some of the hematite is as inclusions, most of it resides at the tips of the hemimorphite crystals. There also appears to be some goethite and limonite present.
no photo
HMI-19
$ 24.00
no photo
HEMIMORPHITE specimen HMI-20
$ 30.00 -20% = $ 24.00
Dims: 1.97x1.44x0.93in (5.01x3.66x2.36cm) .... Wt: 1.17oz (33.0g) .... Loc: Santa Eulalia, Chihuahua, Mexico
Excellent crystals of hemimorphite adorn this specimen. At first I thought the host rock was plates of hematite with limonite, but even using a loupe I could detect no trace of the high luster and crystal faces I'd expect with hematite. Also, the black inclusions and occasional tiny black crystals on the hemimorphite crystals look like goethite, so I'm pretty certain that's what the host rock consists of as well. The hemimorphite crystals are nicely criss-crossed, and spring as radial clusters from a number of starting points
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HMI-20
$ 24.00
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see this List of ALL specimens including SOLD ones
 

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