THE MINERAL BOLEITE

  • Chemistry: Pb26Cu24Ag10Cl62(OH)48 - 3H2O, Hydrated Lead Copper Silver Chloride Hydroxide
  • Class: Halides
  • Uses: A very minor ore of silver, copper and lead and as mineral specimens.
  • Specimens

Boleite is a mineral of crystallographic curiosity and of great interest to collectors of twins, silver minerals and rare halides. And hey . . . its pretty too! Its indigo blue color is distinctive and attractive and some crystals are cut as gemstones. Boleite is technically a tetragonal mineral and as such would form rectangular box-like crystals with a square cross-section. However, boleite is always pseudocubically twinned. In other words, each cube-like crystal of boleite is actually composed of three of these rectangular boxes oriented at right angles to each other. The pseudocubes are sometimes modified by tetragonal dipyramid faces which give the look of octahedral faces. Boleite is sometimes incorrectly listed as an isometric mineral.

Boleite is associated with a couple of other rare halide minerals; cumengite, (Pb21Cu20Cl42 (OH)40) and pseudoboleite, (Pb5Cu4Cl10(OH)8 - 2H2O) These halides have similar chemistries to boleite and often form attached to the boleite crystals as epitaxial overgrowths. The cumengite/boleite combination crystal can form six pointed, 3-dimensional star shapes that are truly amazing.

These halides and others with similar chemistries belong to a division in the Halide Class called the Oxyhalides and Hydroxyhalides. These minerals have either oxygen or hydroxide groups in their chemistries. The oxygen atom in their chemistries might require their classification in the Oxides Class of minerals except that their structures are more tied to the halide elements and the oxygens and hydroxides are kind of superfluous to the overall structure. Some other members of the Oxyhalides and Hydroxyhalides include bideauxite, chloroxiphite, kelyanite, botallackite, laurionite, paralaurionite, mendipite, fiedlerite, pinchite, penfieldite, yedlinite, atacamite, koenenite, diaboleite, zirklerite and paratacamite. Of these, only atacamite and boleite are common enough to be seen at rock shows and in rock shops with regularity.

Boleite was named for its type locality at Boleo, Baja California, Mexico. The French colonial town of Santa Rosalia was built near the copper mines that extracted copper from the unusual sedimentary copper deposits. Boleite crystals can still be found in these deposits although they are scarce and not easy to find. The chemistry of boleite is often written as the simpler Pb9Cu8Ag3Cl21(OH)16 - H2O. But this is not the most accurate portrayal of its chemistry. With its pretty color, valuable and interesting chemistry, rarity, history, associations and twinning; boleite is certainly a "must have" for any serious collector.

PHYSICAL CHARACTERISTICS:

  • Color is deep blue almost black to a lighter indigo blue.
  • Luster is vitreous to pearly.
  • Transparency: Crystals are usually translucent but some exceptional specimens are transparent.
  • Crystal System is tetragonal; 4 2 2
  • Crystal Habits include a pseudocubic habit due to penetration twinning of three individual "twins" oriented perdendicular to each other. Often the crystal will appear to be modified by octahedron faces (actually pseudo-octahedral tetragonal dipyramids). The cubes are rarely over half an inch on each side. Individual twinned crystals are common and are often found loose without any host matrix.
  • Cleavage is perfect in one direction.
  • Fracture is uneven and brittle.
  • Hardness is 3 - 3.5
  • Specific Gravity is 5+ (rather heavy for translucent minerals).
  • Streak is light greenish-blue.
  • Other Characteristics: Notches or interpenetrant angles can be seen in some specimens revealing their true twinned nature.
  • Associated Minerals include other rare copper and lead chlorides such as pseudoboleite, cumengite, chloroxiphite, paralaurionite, matlockite, chlorargyrite, bideauxite, atacamite, mendipite and diaboleite. Also found with cerussite, smithsonite, leadhillite, linarite, phosgenite and chrysocolla. Boleite crystals are often loose, but some are found in a clay matrix.
  • Notable Occurrences include Boleo, Santa Rosalia, Baja California, Mexico; Broken Hill, New South Wales, Australia; Mammoth District, Arizona, USA and Mendip Hills, Somerset, England.
  • Best Field Indicators are crystal habit, color, density, streak and locality.
BOLEITE specimens:
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BOLEITE specimen bol-3
$ 40.00
Dims: 0.4" x 0.3" x 0.3" (1.0 x 0.8 x 0.8 cm)
Wt: 1.3 g
Boleo, Baja California, Mexico
This specimen consists of a small amount of pale brown host rock that is attached to the largest Boleite cube that I have ever seen. This crystal has dimensions of 0.3 x 0.3 x 0.3" (0.8 x 0.8 x 0.8 cm), and is in excellent condition, showing no detectable damage. It has a deep blue color and a pearly-to-vitreous luster, and is dimly translucent along its edges, which show what appear to be small secondary, "stepped" faces. There are a few areas of irregular growth visible on the piece, which remind me of some of the formations that one may see on a cubic fluorite crystal. Though Boleite is listed as forming tetragonal crystals, there are some sources that maintain that its crystals are actually cubic in nature.
no photo
bol-3 ($ 40.00)
Boleo, Baja California, Mexico
BOLEITE specimen bol-4
$ 25.00
Dims: 0.1 x 0.1 x 0.1" (3 x 3 x 3 mm)
Wt: 0.2 g
Amelia Mine, Santa Rosalia, Baja, California, Mexico
This tiny specimen consists of two intergrown pseudocubic Boleite crystals, one of which is much larger than the other. Both are in excellent condition, showing no human-induced damage. The larger cube makes up the dimensions of the entire specimen, while the smaller cube is mostly intergrown and would, if complete, measure 2mm in all dimensions. They show excellent form and have well-defined edges and clean faces that possess a pearly-to-waxy luster. Their blue color is so deep that even under a bright halogen light, one can only see a dim translucence along the crystals' edges. There is no host rock present on this piece.
no photo
bol-4 ($ 25.00)
Amelia Mine, Santa Rosalia, Baja, California, Mexico
BOLEITE specimen bol-5
$ 60.00
Dims: 0.3 x 0.3 x 0.3" (8 x 8 x 8 mm)
Wt: 10.3 g w/ specimen box
Amelia Mine, Santa Rosalia, Baja, California, Mexico
This small thumbnail specimen consists of a single pseudocubic Boleite crystal. This crystal is the largest that I have yet seen in my travels, and though it shows some noticeable damage, it is still in good condition. Its form appears to be cubic, but many sources say that this mineral is tetragonal in nature. Its edges are well-defined and its faces are clean, possessing a bright pearly luster. The size of the crystal and its deep blue coloration prevent all but a faint translucence from showing around its edges in strong light. There is a triangular imprint on one face where another crystal partly intersected this one. There is no host rock present, and the specimen is affixed inside a plastic specimen box with an adhesive putty.
no photo
bol-5 ($ 60.00)
Amelia Mine, Santa Rosalia, Baja, California, Mexico
BOLEITE specimen bol-6
$ 25.00
Dims: 0.1 x 0.1 x 0.1" (3 x 3 x 3 mm)
Wt: 9.0 g w/ specimen box
Amelia Mine, Santa Rosalia, Baja, California, Mexico
This simple, tiny specimen consists of a single pseudocubic Boleite crystal. This crystal is in excellent condition, showing only one spot of noticeable damage, and has excellent form, with well-defined edges and clean faces that possess a pearly-to-waxy luster. It has the classic deep blue coloration and is effectively opaque in normal light. There is no host rock present, and the crystal is affixed inside a plastic specimen box with an adhesive putty.
no photo
bol-6 ($ 25.00)
Amelia Mine, Santa Rosalia, Baja, California, Mexico
BOLEITE specimen bol-7
$ 30.00
Dims: 0.1 x 0.1 x 0.1" (0.3 x 0.3 x 0.3 cm)
Wt: 8.6 g w/ specimen box
Amelia Mine, Santa Rosalia, Baja, California, Mexico
This very small specimen consists of a single Boleite cube. It is in good condition, showing only moderate damage, and has excellent form, with well-defined edges and clean faces. It has the classic deep blue color of its species and a dull waxy luster, and is only dimly translucent under bright halogen light. There is no host rock present, and it is affixed to a small piece of wood which is attached to the bottom of a plastic specimen box.
no photo
bol-7 ($ 30.00)
Amelia Mine, Santa Rosalia, Baja, California, Mexico
BOLEITE specimen bol-8
$ 60.00
Dims: 0.1 x 0.1 x 0.1" (0.3 x 0.3 x 0.3 cm)
Wt: 8.9 g w/ specimen box
Amelia Mine, Santa Rosalia, Baja, California, Mexico
A single cube-shaped Boleite crystal makes up this specimen. It is in nearly pristine condition, showing almost no visible damage, and has excellent form, with well-defined edges, clean faces, and tiny secondary faces that truncate each corner. Its azur-blue color is so dark as to be nearly opaque in normal light, and it has the standard pearly luster. There is no host rock, and it is affixed inside a plastic specimen box with a hot glue.
no photo
bol-8 ($ 60.00)
Amelia Mine, Santa Rosalia, Baja, California, Mexico
BOLEITE specimen bol-9
$ 48.00
Dims:2.0x1.2x0.7" (5.1x3.0x1.8 cm)
Wt: 0.7oz. (21g)
Santa Rosalia, Baja California, Mexico
A small (0.1", 0.3cm) penetration twin crystal of boleite rest on a friable matrix. Also associated are several large (to 0.6", 1.5cm) crystals of feldspar. These feldspars appear to be variety sanidine. There is no damage to the boleite, although the matrix all about it is cracked. A cavity on one end of the matrix shows where another very large sanidine crystal once was.
no photo
bol-9 ($ 48.00)
Santa Rosalia, Baja California, Mexico
BOLEITE specimen bol-10
$ 85.00
Dims: 2.60x1.93x2.20" (6.6x4.9x5.6 cm)
Wt: 4.86 oz. (137.6g)
Santa Rosilia Mine, Baja California, Mexico
This hand specimen has a half-dozen boleite crystals along with quite a bit of massive paratacamite on a matrix too soft to be called siltstone. Three of the boleite crystals are quite good (the largest is about 4mm along its longest dimension). These crystals are deep blue and dimly translucent. This specimen is very fragile (due to the nature of the sedimentary matrix), and handling should be minimized.
no photo
bol-10 ($ 85.00)
Santa Rosilia Mine, Baja California, Mexico

 


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