THE MINERAL NATIVE SELENIUM

  • Chemistry: Se, Elemental Selenium
  • Class: Elements
  • Subclass: Semi-metals
  • Uses: Only as mineral specimens.
  • Specimens

Selenium is a very rare mineral. It is scarce wherever it is found and it is not found too often. The color is a distinctive red-gray with a metallic luster. This is quite different from its closest related element, sulfur, which is vitreous and yellow. It is more similar in color to native tellurium which follows selenium in the same Periodic Table of Elements column. Elements found in the same column of the Periodic Table of Elements tend to have similar properties although those properties also tend to strengthen or diminish either up or down the column.

8 O

OXYGEN
16 S

SULFUR
34 Se

SELENIUM
52 Te

TELLURIUM
84 Po

POLONIUM

On the left is the column from the Periodic Table of Elements in which selenium appears. The farther down the column, the more metallic in character the element becomes. So that oxygen is the least metallic and polonium is the most metallic of the elements in this column. The dividing line between metals and non-metals is between selenium and tellurium; making these elements semi-metals, an element that has significant characteristics of both metals and non-metals. Tellurium is more metallic in nature than selenium but is still a semi-metal.

Although selenium has a metallic luster, it is not metallic in crystal structure or bonding characteristics. Its bonds are more covalent in nature and its structure is more spread out than in metallic minerals such as copper and iron. Both of these elements have lighter atoms than selenium and yet in crystalline form each is nearly twice the density of crystalline selenium. With metallic bonded crystals, atoms are comparatively much closer and are nearly in contact with each other with respect to covalently bonded crystals.

The element selenium has many industrial uses. Most notable is the use of selenium for photvoltaic and photoconductive purposes. This makes it valuable for use in photoelectric cells and exposure meters for photographic purposes. Selenium is also a good tracer element for medical purposes and as a isotope tracer in ground water for hydrogeologic purposes since there are as many as six stable natural isotopes of selenium. The more isotopes, the more control a scientist has over aberrant abundances.

Most elemental selenium comes from the refining of copper sulfides as selenium is a common trace element in these minerals. There is no real ore of selenium as these minerals, including native selenium, are far too rare. These are some other minerals that contain selenium as a major component:

  • Berzelianite (Copper Selenide)
  • Clausthalite (Lead Selenide)
  • Eucairite (Silver Copper Selenide)
  • Hakite (Copper Mercury Silver Antimony Selenium Sulfide)
  • Klockmannite (Copper Selenide)
  • Palladseite (Palladium Selenide)
  • Penroseite (Nickel Selenide)
  • Selen-tellurium (Selenium Tellurium)
  • Tiemannite (Mercury Selenide)
  • Umangite (Copper Selenide)

Selenium the mineral, or native selenium, does not usually form good crystals but when it does they are steep rhombohedrons or tiny acicular (hair-like) crystals. Massive specimens are also known. Selenium is an interesting element that rarely forms good specimens. A specimen of good quality is therefore a real treat for a collector of native elements.

PHYSICAL CHARACTERISTICS:

  • Color is reddish-gray to red.
  • Luster is metallic.
  • Transparency is opaque.
  • Crystal System is trigonal; bar 3 2/m
  • Crystal Habits include steep rhombohedrons or tiny acicular (hair-like) crystals. Massive specimens are also known..
  • Streak is gray.
  • Hardness is 2
  • Specific Gravity is 4.8 (average for metallic minerals).
  • Notable Occurrences include Jerome, Yavapai County, Arizona; Gold Quarry Mine and Willard Mine, Nevada and the Darwin Mine, California, USA; Moctezuma, Sonora, Mexico; Monte Vesuvius, Italy; Harz Mountains, Germany; Potosi, Bolivia and Los Llantenes, Argentina.
  • Best Field Indicators are color, density, hardness and locality.
SELENIUM specimens:
(hover for more info)
SELENIUM specimen sel-1
$ 40.00
Dims: 2.0 x 1.3 x 1.0" (5.1 x 3.3 x 2.5 cm)
Wt: 1.68 oz. (47.9 g)
Darwin Mine, Inyo County, California, U.S.A.
This small thumbnail specimen consists of a quartz-and-pyrite base on which rests a thin crust of Native Selenium. This crust shows no visible crystal form and is only discernable by its dark, violet-gray coloration. It is dull in luster and likely opaque. It coats a few botryoidal quartz formations that are on the piece and is accompanied by a few broken chalcopyrite crystals, along with the pyrites that are embedded in the quartz.
no photo
sel-1 ($ 40.00)
Darwin Mine, Inyo County, California, U.S.A.
SELENIUM specimen sel-2
$ 50.00
Dims: 1.9 x 1.3 x 0.9" (4.8 x 3.3 x 2.3 cm)
Wt: 1.8 oz. (51.9 g)
Darwin Mine, Inyo County, California, U.S.A.
Two very thin crusts of massive Selenium rest on the quartz-and-pyrite base of this small hand specimen. The Selenium is easy to see, as it has a dull, deep violet color. It shows no apparent crystal form and no visible metallic tendencies. A few pyrite crystals are also visible, but most of these are damaged.
no photo
sel-2 ($ 50.00)
Darwin Mine, Inyo County, California, U.S.A.
SELENIUM specimen sel-3
$ 37.50
Dims: 2.4 x 2.0 x 1.7" (6.0 x 5.1 x 4.3 cm)
Wt: 4.9 oz. (140 g)
Defiance Workings, Darwin Mine, Darwin, Inyo County, California, U.S.A.
A few very thin crusts of Native Selenium rest on the pyrite base of this hand specimen. These crusts are very thin and show no evidence of visible crystals. They have a dull, dark violet color and a dull matte luster, and coat a few areas of the base. The pyrite base shows rather bad crystal form, and appears to contain some quartz, also.
no photo
sel-3 ($ 37.50)
Defiance Workings, Darwin Mine, Darwin, Inyo County, California, U.S.A.
SELENIUM specimen sel-4
$ 71.00
Dims: 1.5x1.4x0.7" (3.9x3.7x1.7 cm)
Wt: 0.87 oz. (24.7g)
Katherina Mine, Radvanice, Czech Republic
This nondescript gray rock has a sparkle, entirely due to needles of the element selenite. These look entirely metallic gray - there is no hint of a reddish tone. Close examination shows that much of the one side of the specimen has these acicular crystals embedded in the brown-gray host rock.
no photo
sel-4 ($ 71.00)
Katherina Mine, Radvanice, Czech Republic
SELENIUM specimen sel-5
$ 27.00
Dims: 0.8x0.6x0.5" ( 2.0x1.5x1.3cm)
Wt: 7.9ct (1.58g)
Shcoeller Mine, Kladne, Czech Republic
This small thumbnail specimen features native selenium in two forms. The specimen is partially coated with a crust of redish native selenium showing no crystal form. Also, there are several tiny, metalic, reddish-gray crystals which are another form of the element. There are other minerals (notably black cubes) which may be another rare selenium mineral, but I have not identified them. The specimen was broken by my examination - both pieces are included.
no photo
sel-5 ($ 27.00)
Shcoeller Mine, Kladne, Czech Republic
SELENIUM specimen sel-6
$ 35.00
Dims: 1.06x0.64x0.36" (2.69x1.62x0.92cm)
Wt: 0.03oz (0.8g)
Schoeller Mine, Kladno, Czech Republic
This specimen, although very small, displays some of the best selenium crystals I have seen. They do not really have a red color, but rather they appear black. At first, I thought they were organized as sprays of acicular crystals, but a loupe and careful examination reveals that the individual crystals have a steep rhombohedral shape, and only the tips have enough translucency to detect a hint of red. Overall, the crystals appear nearly black, with a good metallic luster. There are a lot of these crystals - all of the sparkle on the specimen is due to them.
no photo
sel-6 ($ 35.00)
Schoeller Mine, Kladno, Czech Republic
 

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