Sphalerite
Authors: Jessica Haggith, Tiffany Barrera, Trent Hannemann
Mineral Name: Sphalerite (Blende)
Chemical Composition: (Zn, Fe)S it is zinc sulfide with less than 25% iron. (2)
Color: Charcoal gray, but can be yellowish, brown, black, red, green, white and colorless. It may be transparent or translucent. (2)
Streak:The streak is light yellowish to brown in color. But for pure Sphalerite the streak is actually clear in color.
Hardness: 3.5-4, this means that the mineral is strong enough to scratch a penny but the mineral is not strong enough to scratch glass or a nickel-plated nail.
Cleavage/Fracture: Cleavage is dodecahedral in 6 directions of perfect cleavage, and fracture is conchoidal meaning it resembles the shape of a scallop shell. (3, 1)
Crystal Form: Most commonly, sphalerite is found shaped as tetrahedral crystals, with a pyramid-type shape. The crystal faces are usually somewhat rounded or curved. Sometimes closely resembling octahedral crystals (8-sided crystals that look like 2 pyramids attached at their base) or can be found in association with distorted dodecahedral (10-sided crystals) and cubic crystals (6-sided crystals). Sphalerite crystals can look or be gritty in texture or feel, botryoidal (resembling a cluster of grapes), stalactitic (type of formation that hangs from ceilings of caves,hot springs) and even enormous in size. It is of the isometric crystal system. The crystal form of sphalerite could be in a cubed form. (3) The crystal habits of sphalerite are somewhat difficult to discern with the rhombic, dodecahedron, tetrahedron and the mixing of these two attributes having cubic and tetrahedron giving it multiple faces with different forms.
Luster: Metallic to Adamantine
Special Features: Sphalerite ranges from a gem like transparent crystal all the way to a black, metallic, opaque luster. (3) It also has six cleavage plains, which is very uncommon. This type of mineral is triboluminescent, which means if the mineral is crushed it will glow in the dark.(4) It is also pyroelectric meaning when it is heated or cooled it gives off a slight electrical charge. (4) It can be transparent, even translucent sometimes and will fluoresce orange in shortwave ultraviolet light. (3)
Class sample: Sphalerite is a super shiney mineral and was black/grey in color with many sparkles and fine granules throughout the mineral. It is rough with smooth spots. This mineral is cold to the touch and has a moderately heavy feel to it.
Varieties: Cleiophane is a lightly colored to transparent variety of Sphalerite. (3) Schalenblende is a banded form of sphalerite. (3) There are two varieties that are generally not used or accepted by all and are subject to an author's need to explain further; those would be Marmatite, an opaque, metallic, and iron rich variety of sphalerite, and Ruby Jack a Red colored type of sphalerite that is transparent to translucent. (3)
Mineral Group: Sphalerite is part of the sulfides, which is a group of minerals that are made up of one or more metallic minerals combined with the nonmetallic element sulfur. It is also part of the simple sulfides, which is a group where the minerals contain one or more true metal combined with sulfur. (3)
Environment: Sphalerite can be found where hydrothermal activity or contact metamorphism occurs bringing zinc-bearing fluids that are hot and acidic in contact with carbonate rocks. Sphalerite is frequently associated with the minerals galena, dolomite, calcite, chalcopyrite and marcasite deposits (cite).
Associated Rock types: Sphalerite is found in sedimentary limestone deposits. Sphalerite is occasionally found in basalts.
Occurrence in North America: Sphalerite is found in In North America it can be found in Alaska, Idaho, Missouri, Illinois, New York, Colorado and Tennessee. (2)
Economic Uses: Sphalerite is used for jewelry. Though this mineral is not very precious, it is a very beautiful show piece due to its high level of light dispersion, which is three times higher then the dispersion of diamonds. Sphalerite has the dispersion of 0.156. Dispersion is the separation of white light as it passes through the mineral to disperse flashes of colors in the color spectrum.
Industrial Uses: Sphalerite is a very common mineral mined for its zinc. It is found underground in long layered veins that form underground. Extracted sphalerite is mainly used to make usable, industrial metals. Some of the metals are galvanized iron and brass, and is used in batteries. Sphalerite is an important compound as it is used to make various rubbers and paint products, as well as medicines and chemicals.(8)
First Notable Identification: Sphalerite was first discovered in 1846 by a scientist named Ernst Friedrich Glocker (1793–1858). (6) The word sphalerite is from the Greek language, ‘sphaleros”, meaning “to deceive or be treacherous”. The mineral was given this name because of the many different appearances of sphalerite causing miners to have a tough time identifying the mineral and confusing it with other types of minerals. This mineral is frequently difficult to identify. (2)
How We Identified It: The way we identified sphalerite is by using the scratch test for hardness. We also tested the color of the streak and we properly identified the cleavage planes. With 6 being rare, it narrowed down the search.
Don’t Confuse It With: Sphalerite has a wide variance in color and it has been confused with many other minerals over the years. Acanthite/Argentite is a silver sulfide and they share a common color grey to black and have a similar crystal system The fracture in both is conchoidal, but in sphalerite it is rarely seen because of the clear cleavage. The streak is also quite different in argentite is a shiny black where sphalerite yellow to light brown. (4) Tetrahedrite is another sulfide and is the ore of copper, whereas sphalerite is the ore of zinc. It to is the a similar color of black to steel gray even silver, it also has a conchoidal fracture but again cleavage is not present and it has a streak of black to brown, which is a good way to tell the difference in the field, along with the lack of cleavage. (4) Galena is a sulfide and is the major ore of lead and silver. It too is a silver gray, but sometimes has a bluish tint. The crystal system is isometric too, and it also has spinel twinning but the cleavage plains present in the galena is a perfect three, not six, directions. Galena’s streak is a definite gray and it is a very dense material making it considerably heavier feel than sphalerite. (4) Magnetite is the major ore of iron. It too is black in color and is metallic to dull and the crystals are opaque as is common sphalerite. Magnetite is very hard, in comparison to sphalerite, and the streak is black, unlike sphalerite. However, the easiest way to tell you have magnetite is touch it to steel or iron as it is magnetic. (4) Fluorite, part of the halides group and is a gemstone that has a very multicolored spectruma and can be seen in many of the same colors as sphalerite, except black and gray, and has a glass-like appearance similar to sphalerite in the gemstone form. However, fluorite only has perfect cleavage in 4 directions, not 6 like sphalerite and it is rather brittle and light in the hand comparatively. (4)
Bibliography:
1.Michelle, Meg. “Important Uses of Sphalerite.” Sciencing, Leaf group Ltd., 14 Apr. 2017, sciencing.com/important-uses-sphalerite-5044698.html. Basic info Sphalerite.
2. King, Hobart M. “Sphalerite.” Geology, Geology.com, geology.com/minerals/sphalerite.shtml. Basic Info about Sphalerite.
3. “Minerals.net.” Sphalerite blende: The mineral sphalerite information and pictures, Hershel Friedman and Minerals, www.minerals.net/mineral/sphalerite.aspx. Very good photos on this
site.
4.“THE MINERAL SPHALERITE.” SPHALERITE (Zinc Iron Sulfide), www.galleries.com/Sphalerite.
5.The Mineral and Gemstone Kingdom, www.minerals.net/mineral/sphalerite.aspx.
6.“THE MINERAL SPHALERITE.” SPHALERITE (Zinc Iron Sulfide), Amethyst Galleries, Inc, 2014, www.galleries.com/Sphalerite.
7.“Ernst Friedrich Glocker.” Wikipedia, Wikimedia Foundation, 17 Feb. 2018,
en.wikipedia.org/wiki/Ernst_Friedrich_Glocker.
8. King, Hobert M. Geology.com. IRONdb, 2015. Web. 14 Mar. 2018.
9.Kirmayer, Andy. "HOW IS SPHALERITE MINED." Career Trend, 5 July 2017. Web. 14 Mar. 2018.