THE MINERAL TENNANTITE
- Chemistry: Cu12As4S13, Copper Arsenic Sulfide
- Class: Sulfides
- Group: Tetrahedrite
- Uses: ore of copper and a minor ore of silver and arsenic.
Specimens
It is difficult to distinguish the two minerals by ordinary means. Tennantite is generally darker, has a redder streak and a translucent red color that can be seen in thin splinters when they are held up to a strong light. Tetrahedrite is by far the more common of the two. Tetrahedrite is named for the common form, the tetrahedron, that both tennatite and tetrahedrite form.
The tetrahedron is an interesting isometric crystal form. It is obvious where the four three fold axes of the isometric system belong, as each one exits out of the crystal through each of the four identical "pyramidal" peaks. However the four fold axes are evidently missing. They aren't, they are just four fold rotoinversion axes. A four fold rotoinversion axis takes a face, rotates it 90 degrees (one fourth of a rotation) and then inverts it (up to down & right to left) through the crystal to the other side. Then it rotates it again 90 degrees and inverts it again through the crystal. Another rotoinversion operation and finally another (four in all) and the face is back, exactly where it started. The result is two faces on the "top" and two on the "bottom" of the crystal but in perpendicular orientation. The tetrahedral faces of tennantite are in many instances modified by other crystal forms giving the crystals multiple facets while still retaining the overall tetrahedral shape.
Tennantite is in an informal group of minerals called the "fahlerz" or "fahlores" group. The group is named for an old german miners word meaning "pale ore". Most members of the tetrahedrite group belong to this informal group.
Although rarer than its cousin, tennantite forms nice crystals and can be a handsome specimen. Often tennantite will contain a certain percentage of silver and be used as a minor ore. Collectors usually crave nice specimens of verified tennantite.
PHYSICAL CHARACTERISTICS:
- Color is black to steel gray.
- Luster is metallic.
- Transparency crystals are opaque.
- Crystal System is isometric; bar 4 3m
- Crystal Habits of course include the tetrahedron sometimes modified by the dodecahedron and tristetrahedron. Twinning is occassionally seen. Also massive and granular.
- Cleavage is absent.
- Fracture is subconchoidal.
- Hardness is 3 - 4.
- Specific Gravity is approximately 4.6 (average for metallic minerals)
- Streak is black to reddish if rubbed.
- Associated Minerals are quartz, pyrite, arsenopyrite, chalcopyrite and other sulfides.
- Other Characteristics: thin splinters can have a translucent red color.
- Notable Occurances include Bennatal, Switzerland; Tsumeb, Namibia; Saxony, Germany and Butte, Montana, USA.
- Best Field Indicators are crystal habit, lack of cleavage, streak and color.
 Amethyst Galleries' Mineral Gallery MINERALS |
TENNANTITE specimen ten-1
$ 30.00
$ 30.00
Dims: 2-1/4" x 1-1/2" x 3/4"
Wt: 2.6 oz
Hulcani, Peru
Though not perfectly formed, this is a large piece of crystalline Tennantite, with very little else accompanying it. It is a dark gray, metallic color with some subtle but noticeable irridescence on some of the minor faces. There are a few complete crystal faces, but several crystals had originally fused together so that none are discernable as being complete and independant. There is a light dusting of quartz on a portion of it, and a few larger crystals that have their terminations buried in their "host." This is evident because there is a hexagonal hole where one of the crystals was pried out. It's a beautiful and unusually large single piece of Tennantite.
ten-1 ($ 30.00)
Hulcani, Peru
TENNANTITE specimen ten-2
$ 45.00
$ 45.00
Dims: 3.1" x 2.7" x 1.8"(7.9 x 6.9 x 4.6 cm)
Wt: 15.7 oz.(444 g)
Hulcani, Peru
The oddest aspect of this cluster of Tennantite crystals is their individual form. These things look like metallic garnets! I believe they occur in a complex form like a deltoid dodecahedron, but they are quite small, somewhat warped, and their edges are indefinite, so I can't really define their form. They are small(a bit larger than 1/8"[3-4 mm] in diameter) and have a dark gray color and metallic luster. They cover a layer of what seems to be both pyrite and chalcopyrite that has a few visible crystals and is over 1"(2.5 cm) thick. Under that is another layer of Tennantite, with only a few crystal faces being definable.
ten-2 ($ 45.00)
Hulcani, Peru
TENNANTITE specimen ten-3
$ 45.00
$ 45.00
Dims: 3.4" x 3.4" x 1.8"(8.6 x 8.6 x 4.6 cm)
Wt: 14.7 oz.(416 g)
Hulcani, Peru
This specimen is mostly Tennantite by weight. It has the standard dark gray color, metallic luster and opacity of its kind, but the shape confuses me a bit. It is definitely in a form closely related to the tetrahedron, but each of its points are truncated by 3 short, secondary termination faces that "round off" each crystal. The largest discernable crystal that I could find on the piece is about 1/4"(6 mm) along an edge. There are also a small number of chalcopyrite crystals scattered among the Tennantites. There is substantial damage to the crystals, but I believe most of this occurred when the specimen was being taken from its native environment, as it occurs primarily along the specimen's edges.
ten-3 ($ 45.00)
Hulcani, Peru
TENNANTITE specimen ten-4
$ 75.00
$ 75.00
Dims: 5.5 x 3.5 x 1.5" (14.0 x 8.9 x 3.8 cm)
Wt: 1 lb., 11.4 oz. (776 g)
Hulcani Mine, Ancash Department, Peru
This large hand specimen consists primarily of a crust that is made up of hundreds of small, intergrown Tennantite crystals. These crystals generally do not exceed 0.1" (3 mm) in diameter, but are generally in excellent condition- damage is limited to the edges of the crust. All are heavily intergrown, so none are complete, and magnification is needed to effectively examine their form. However, their form is quite good, given the circumstances, and most of the crystals have a definite cubic form- a few show some octahedral faces. All have the moderate gray color and metallic luster that is standard for this mineral. Accompanying the Tennantite are scores of tiny bladed crystals that are colorless, transparent, and very clear. They are not made of calcite, as I have done an acid test on a tiny piece. I really do not know what they are composed of.
ten-4 ($ 75.00)
Hulcani Mine, Ancash Department, Peru
TENNANTITE specimen ten-5
$ 105.00
$ 105.00
Dims: 2.5 x 2.5 x 1.5" (6.4 x 6.4 x 3.8 cm)
Wt: 6.4 oz. (182.2 g)
Dzhezkazgan, Kazakhstan
Scores of heavily intergrown Tennantite crystals make up the bulk of this small hand specimen. The largest of the crystals on this piece has dimensions of 0.8 x 0.7 x 0.5" (2.0 x 1.8 x 1.3 cm) most are in excellent condition, though there are several that are visibly damaged. All have very warped form due to their intergrowth and none are isolated or integral. Those visible edges are well-defined, however, and their faces are generally flat and clean. All have a dark gray coloration and a dull metallic luster. The crust that the Tennantites form appears to have grown over a base of chalcopyrite, enveloping most of it. However, a few warped and heavily intergrown crystals are visible, with their standard deep orange-golden coloration and metallic luster. Besides these, there are no other minerals or any host rock present.
ten-5 ($105.00)
Dzhezkazgan, Kazakhstan
TENNANTITE specimen ten-6
$ 95.00
$ 95.00
Dims: 5.5 x 4.6 x 1.4" (14.0 x 11.7 x 3.6 cm)
Wt: 1 lb., 14.0 oz. (850 g)
Hulcani Mine, Ancash Department, Peru
This flat cabinet specimen consists of several dozen warped, heavily-intergrown Tennantite crystals that coat a thin, crystalline pyrite crust. The Tennantites are so heavily intergrown that it is difficult to assess their sizes, but most appear to measure between 0.2 and 0.4" (0.5 and 1.0 cm) in diameter. They are in good condition, though several of the most exposed points show some damage. All are so heavily intergrown that their complex, cube-based forms are almost unidentifiable; however, I do see faces that correspond to complex variations of either the tristetrahedron or the deltoid dodecahedron, or perhaps both. All have a moderately dark gray coloration and a dull metallic luster. Several pyritohedral pyrite crystals peek through among the Tennantites- none of these are exposed enough for good study, but the largest likely have diameters of 0.7 to 0.8" (1.8 to 2.0 cm), and all have excellent form, with well-defined edges and clean, lightly striated faces that possess the standard pale golden color and metallic luster of this mineral. These sulfide minerals are accompanied by scores of tiny siderite crystals which range in diameter from 1 mm up to 0.3" (8 mm). They occur either as trigonal tabular "nailheads" or as rounded nodules. All have a pale brown color and a dull waxy luster, and are opaque. They are scattered on top of the Tennantite and pyrite on one side of the specimen, and are are highly intergrown into a crust that coats most of the other side of the pyrite base.
ten-6 ($ 95.00)
Hulcani Mine, Ancash Department, Peru
TENNANTITE specimen ten-7
$ 60.00
$ 60.00
Dims: 2.5 x 2.0 x 1.9" (6.4 x 5.1 x 4.8 cm)
Wt: 5.5 oz. (156.5 g)
Dzhezkazgan, Kazakhstan
Countless intergrown Tennantite crystals make up the bulk of this small hand specimen, and actually create sort of a "base rock". The crystals are generally in good condition, as there are several areas that have noticeable damage. If complete and integral, the largest crystals would measure 0.3 - 0.4" (0.8 - 1.0 cm) and would have reasonably a reasonably good tetrahedral form. All have a dark gray coloration and a moderately dull metallic luster. A crust of tiny quartz crystals covers a portion of the Tennantite base- the crystals do not exceed 0.3" (8 mm) in length and have good form. The base also contains several chalcopyrite crystals that are integrown into 3 or 4 groups. They show considerable damagae, but have excellent tetragonal form where they are intact. Their deep golden coloration and moderate to dull metallic luster is standard.
ten-7 ($ 60.00)
Dzhezkazgan, Kazakhstan
TENNANTITE specimen ten-8
$ 150.00
$ 150.00
Dims: 2.24x2.13x1.26" (5.7x5.4x3.2cm)
Wt: 4.17oz. (118.0g)
Julcani Mine, Angaraes, Huancavelica, Peru
This specimen is a pseudomorph - the crystals of tennantite are in the shape of the enargite crystals that initially formed. The large crystals are nearly tablular, as they look like several prismatic crystals formed in parallel. While the overall form of the crystals is that of enargite, there are tiny additional terminations that appear fresh and look like tennantite. There is also a fair amount of brassy pyrite crystals, plus several blades of barite (I believe).
ten-8 ($150.00)
Julcani Mine, Angaraes, Huancavelica, Peru
TENNANTITE specimen ten-9
$ 40.00
$ 40.00
Dims: 0.94x0.67x0.51" (2.4x1.7x1.3cm)
Wt: 0.34oz (9.5g)
Steward Mine, Butte, Montana, USA
This tenantite specimen only shows hints of tetrahedral form, as each tetrahedron has been modified (the points are missing, replaced with a flat face, making the form a distorted octahedron). The color is black, and I cannot see any hints of red translucency.
ten-9 ($ 40.00)
Steward Mine, Butte, Montana, USA
TENNANTITE specimen ten-10
$ 110.00
$ 110.00
Dims: 2.95x2.07x1.29" (7.50x5.27x3.27cm)
Wt: 4.36oz (123.3g)
Mine 57, 180 m level, Dzeskazgan, Karaganda oblast, Kazahkstan
This specimen has 5 good clusters of tennantite crystals. All are complex and distorted, although some display the tetrahedral form that this mineral often takes. The tennantite is very dark silver-gray, nearly black, and the crystals are opaque. Some of the crystals display some green copper compounds, likely due to decomposition of the tennantite (a copper mineral). These crystals rest on a druze of quartz crystals, which appear fairly dark. A loupe reveals that this is due to a very odd looking dusting of brassy mineral, possibly pyrite or chacopyrite, but in a form I have never seen.
ten-10 ($110.00)
Mine 57, 180 m level, Dzeskazgan, Karaganda oblast, Kazahkstan