PHYSICAL PROPERTIES:
Chemistry: (Zn, Fe)S
Composition: Zinc Iron Sulfide
Class: Sulfides
Group: Sphalerite
Crystal system: isometric
Fracture: conchoidal
Hardness: 3.5-4
Specific gravity: 4
Refractive Index: 2.37 - 2.42
Luster: adamantine to resinous
Streak: yellow to light brown
Cleavage: perfect in six directions
Color: black to brown
also yellow to red and very rarely
colorless
Transparency: crystals are transparent to translucent
Associated Minerals: Arsenopyrite,
Barite, Chalcopyrite, Calcite, Dolomite, Fluorite, Galena, Magnetite,
Pyrrhotite, Pyrite, Quartz, Siderite, and many other mineral verities.
COMPOSITION:
6 7.0% Zn, 33.0% S with varying amounts of iron and manganese,
and other elements.
DISTINGUISHING CHARACTERISTICS:
Sphalerite can resemble some galena, the streak and the blowpipe tests
will determine the difference here. It also resembles some siderite,
but can be distinguished by remaining non-magnetic after heating and
also by its higher specific gravity. The characteristic luster and association
with pyrite and galena generally serve to identify sphalerite. Sphalerite's
luster really sparkles. It's unusually high index of refraction
produces a fire greater than diamond's. When rotated good specimens,
with hundreds of small sparkling faces, will produce multiple
bright flashes. Sphalerite's structure is analogous to the diamond
structure. If every other carbon in the diamond structure is replaced
by a sulfur atom and the remaining carbons are replaced with either
a zinc or an iron atom then basically the mineral is sphalerite.
ENVIRONMENT:
In suiphide ore veins in all rock classes.
CRYSTAL DESCRIPTION:
Tetrahedral crystals are very common, some times they
are so completely developed that they look octahedral. Cube, dodecahedron,
and tristetrahedron faces can also be present, the dodecahedron is often
rounded so that it is difficult to distinguish the faces. Sphalerite
can also be stalactitic, granular, and massive. The twinning of sphalerite
is also special. It can form a spinel twin which is a specialty of the
mineral spinel. The spinel twin is where a tetrahedral crystal is twisted
in the middle so that three points of the tetrahedron are in alignment
with the other three points. These crystals are not usually completely
developed in sphalerite but the indentations that the twinning causes
are usually seen on some crystals in almost every specimen. There is
also a twin type called a chicken twin or hen. This twin forms a sort
of football shaped twin.
Sphalerite is a polymorph with two minerals, wurtzite
and matraite. The three are called polymorphs. Which means they have
the same chemistry, (Zn, Fe)S or zinc iron sulfide. But they have different
structures and therefore different shapes. Sphalerite is the more common
mineral of the three. There is also an iron rich variety of sphalerite
that is called Marmatite.
Marmatite is not a commonly seen mineral because it is brilliant black
like black sphalerite.
So it is very often unrecognized. Marmatite is chemically
a ferroan sphalerite. It contains,up to twenty percent iron,
in addition to zinc sulfide.
TESTS:
Practically infusible on charcoal, but gives coating around chip which
is yellow when hot, and white when cold. Touched with cobalt solution,
the yellow coating becomes green in the reducing flame. Also adding
Na,CO, then dissolve in HCL. The bubbles will be H2S
which has a rotten egg smell.
LOCALITIES:
Sphalerite locals are very numerous. We have
some nice specimens from Chihuahua, Mexico. Other notable locals are
the Tri state area near Joplin, Missouri. Joplin crystals range from
black and dull irregular giants to minute red (ruby jack) encrustation's.
Very pale light yellow to green crystals are from Franklin, New Jersey.
Nice Specimens come from Rosiclare, Illinois; Elmwood, Tennessee;
Broken Hill, Australia; Italy; Spain; Burma; Peru; Morocco; Germany
and England.
USES:
Sphalerite is the principal primary ore of zinc.
It alters to hemimorphite, smithsonite, and willemite. The impurities
gallium, indium, and cadmium make it also the chief ore of those metals.
Sphalerite can make a rather attractive specimen as well. On rare occasion
it is cut into a collector only type gemstone.
FACTS & HISTORY:
Black Jack and Ruby Jack are nick names given respectively to the
black and red crystal forms of sphalerite.
An aggregate of botryoidal crusts with layers of wurtzite and galena
is called "Schalenblende" is sometimes cut and polished as an ornamental
stone.
Its cleavage and luminescence make Sphalerite a very interesting
mineral. It is the best example of dodecahedral cleavage (six direction
cleavage). With care, perfect rhombic dodecahedrons can be cleaved out.
Sometimes it fluoresces orange in ultraviolet light. Fluorescent sphalerite
also shows the phenomenon of triboluminescence. Which means it emits
flashes of orange light when struck lightly with a hard substance like
steel or a stone.
The names Sphalerite which is Greek for treacherous
rock and Blende which is German for blind or deceiving. Were names used
by miners because sphalerite can be so difficult to identify from more
valuable minerals such as galena, acanthite and tetrahedrite.
Top
Click here
to see our Specimens
Click here for Sphalerite Group Information
Ruby Jack Sphalerite