THE MINERAL MILLERITE
- Chemistry: NiS, Nickel Sulfide
- Class: Sulfides and Sulfosalts
- Uses: Mineral specimens and as a very minor ore of nickel.
Specimens
The oxide rutile and the silicate elbaite, a tourmaline, are two other minerals that can be mistaken for millerite when they form acicular sprays of crystals. Millerite's environments of formation, mainly in hydrothermal replacement deposits and in limestone and dolomite cavities and associated geodes, usually serve as the best way to distinguish it from the aforementioned minerals.
It is a real bonus to quartz geode collectors from Indiana to Kansas to open up a geode and find a spray of brassy millerite crystals tucked inside. It is postulated that the source of the nickel for the millerite that is found in these geodes is somehow derived from a meteoritic origin. Perhaps nickel, dissolved from iron-nickel meteorites, leached into the geodes by way of ground water and found an environment suitable for the formation of millerite crystals. Speaking of meteorites, millerite is one of several minerals that is routinely found (albeit in scarce quantities) within iron-nickel meteorites.
Millerite is also called "Capillary Pyrite" since it has a brassy yellow color that is close to the color of pyrite and forms the trademark capillary crystals. When found as brassy sprays inside of sparkling clear quartz geodes, millerite can make a wonderfully attractive and interesting mineral.
PHYSICAL CHARACTERISTICS:
- Color is brassy yellow .
- Luster is metallic.
- Transparency Crystals are opaque.
- Crystal System: Trigonal; bar 3 2/m
- Crystal Habits include aggregates of acicular (hair-like) or capillary crystals. The aggregates form radial sprays or randomly dispersed individual hairs. Also seen as fibrous coatings and rarely found in granular masses. Millerite is one of several minerals that is found in iron-nickel meteorites.
- Cleavage is perfect in several directions but is rarely discernible due to the extremely thin crystals.
- Fracture is uneven.
- Hardness is 3 - 3.5
- Specific Gravity is 5.3 - 5.5
- Streak is dark green to almost black.
- Other characteristics: may tarnish to a gray color and crystals can be attacked by acids.
- Associated Minerals
calcite,
quartz,
dolomite,
bravoite (basically a nickel-rich pyrite), chalcopyrite, grossular, fluorite and pyrrhotite. - Other Characteristics: crystals are not flexible and are brittle.
- Notable Occurrencesinclude south central Indiana, Keokuk, Iowa, Gap Mine, Pennsylvania and Sterling Mine, New York, USA; Freiberg, Germany; Glamorgan, Wales, England and Sherbrooke and Planet Mines, Quebec.
- Best Field Indicators crystal habit, associations and environment, color and luster.
 Amethyst Galleries' Mineral Gallery MINERALS |
MILLERITE specimen mil-1$ 250.00
Dims: 2-1/2" x 2" x 1"
Wt: 3.61 oz
Thompson Open Pit, Thompson, Manitoba, Canada
This is a mineral that intrigues me; it is rather mysterious that nickel could become concentrated in such a quantity to create this Millerite specimen! The piece consists of 2 layers that have grown together at one end to create what I would call a "clamshell". The entire interior of this crevice is filled with almost hairlike needles of the material. One side of the exterior is likewise covered with the crystals, but due to exposure there is considerable damage. The cross-section of these layers shows the fibrous nature, dull pyritic color and metallic luster of the needles, which grow up to 1/4 inch long(only the top 1/16 inch of most of the crystals are separated enough so that individuality can be determined. There is no host rock.
mil-1 ($250.00)Thompson Open Pit, Thompson, Manitoba, Canada
MILLERITE specimen mil-2
$ 190.00
$ 190.00
Dims: 1-7/8" x 1-3/4" x 1-1/4"
Wt: 3.26 oz
Thompson Open Pit, Thompson, Manitoba, Canada
Another "clamshell" of Millerite, this specimen is made up of two 3/8-inch rectangular layers of the mineral that have intersected each other at one end at an acute angle, creating a crevice in which grow countless hairlike needles of the nickel sulfide mineral. The exterior face of one of the layers is likewise coated with the needles, and is surprisingly undamaged. Looking down their lengths, these crystals appear to make a dense, dark brown mat. A cross-section of one of the layers reveals the fibrous habit, dull golden color, 1/4-to-1/2-inch length and metallic luster of the crystals. A small amount of noncrystalline quartz is attached to a few spots on the specimen.
mil-2 ($190.00)
Thompson Open Pit, Thompson, Manitoba, Canada
MILLERITE specimen mil-3
$ 150.00
$ 150.00
Dims: 2-1/4" x 1-1/4" x 1/2"
Wt: 1.90 oz
Thompson Open Pit, Thompson, Manitoba, Canada
This Millerite specimen consists of a small slab of the material, one side of which is coated with a dense mat of exposed, hairlike crystals. Looking down on their terminations, the crystals appear to make up a dark brown "fuzz". Looking at the cross-section of the slab, though, one can see that only the top 1/16 inch of the sometimes 1/4-inch-long crystals is exposed, and that their remainders are tightly packed into a solid, dull gold mass with a metallic luster. There are 2 exposed acicular "puffballs" on top of the bed of crystals, and a large one was broken, showing the acicular habit of these fine crystals, creating a beautiful sunburst pattern on one edge of the slab. This is quite a pretty specimen of a not-very-often-found mineral.
mil-3 ($150.00)
Thompson Open Pit, Thompson, Manitoba, Canada
MILLERITE specimen mil-4
$ 225.00
$ 225.00
Dims: 2.7" x 1.6" x 0.5"(6.9 x 4.1 x 1.3 cm)
Wt: 2.58 oz.(73.1 g) w/ base
Thompson Open Pit, Thompson, Manitoba, Canada
This specimen, composed almost entirely of Millerite, consists of a crust that is made up of thousands of tiny needle-like crystals of the material. There is very little damage to the specimen, so it looks like there are beds of brassy, metallic moss on both sides of it. The edges of the specimen are the only points of breakage, and show where the specimen was separated from its place of origin. Examination of this edge shows the Millerite's radial habit and allows one to see that some of the crystals are close to 0.3"(8 mm) long, though only about 0.1"(2 mm) of their tips are visible. They have a dark, brassy color, a metallic luster, and are opaque. There are a few small, broken shards of what appear to be quartz on one side of the specimen, which also seems to show some massive Millerite, but it could be another metallic sulfide. The specimen is glued upright onto a square acrylic base so that both sides can be seen easily.
mil-4 ($225.00)
Thompson Open Pit, Thompson, Manitoba, Canada
MILLERITE specimen mil-5
$ 57.00
$ 57.00
Dims: 3.7 x 2.3 x 1.2" (9.4 x 5.8 x 3.0 cm)
Wt: 7.90 oz. (224.1 g)
Halls Gap, Lincoln County, Kentucky, U.S.A.
This hand specimen consists of several small "mattings" of fine, interlaced Millerite needles rest in part of a geode that is still partly embedded in the shale host rock of this hand specimen. Given the fact that each needle is finer than a human hair, assessment of damage and crystal form is nearly impossible. All have the dull, brown-gold coloration and metallic luster that are standard for Millerite, and achieve lengths of up to 0.5" (1.3 cm) and possibly more. They rest amid small flat and botryoidal formations of quartz that line the interior of the geode. A friend mine and I went to Halls Gap 2 weeks ago to try to find some of these- however, I think that the deep hollow wherein they are found was blasted because it was unsafe. We found many geodes, but none that contained Millerite.
mil-5 ($ 57.00)
Halls Gap, Lincoln County, Kentucky, U.S.A.
MILLERITE specimen mil-6$ 450.00
Dims:5.4x3.2x2.0" (13.7x8.1x5.1 cm)
Wt: 24.8oz. (703g)
Thompson Open Pit, Thompson, Manitoba, Canada
This is easily the most impressive specimen of millerite I have ever seen. A solid crust of millerite to 0.3" (0.8cm) thick covers the entire top surface (part of the bottom, as well) of this specimen. On the bottom, veins of millerite may be seen in the rock, along with a small amount of massive calcite. Scattered over the top of the specimen are several stalagmites that are tipped with tiny clusters of pyrite crystals. This is extremely aesthetic. The only damage to this specimen are the edges, where it was broken away from the host rock. All I can say is "Wow!"
mil-6 ($450.00)Thompson Open Pit, Thompson, Manitoba, Canada
MILLERITE specimen mil-7$ 263.00
Dims: 1.7x1.1x1.6" (4.3x2.9x4.0 cm)
Wt: 1.54 oz. (43.5g)
Thompson Open Pit, Thompson, Manitoba, Canada
This millerite specimen is very appealing, in that it is not just a flat specimen. Two different pieces of host rock are held together by intergrown millerite crystals, which also grow around and over the front piece. The millerite (metallic green crystals with a velvety appearance) has excellent form and shines with a bright metallic luster where the edges are exposed. A small portion of the front has another mineral (looks like pyrite) as a crust of tiny crystals. The two host rocks are of different compositions. The back rock is a light green somthing cementing thousands of tiny transparent crystals together (I suspect they are pale grossular garnet crystals). The front host rock is a dark greenish-black something cementing some transparent red crystals and pyrite together. It also hosts some larger (4mm) assemblage of red transparent crystals, likely more grossular. These can only be examined with a loupe. There are two small areas that look like damage on the front of the millerite, although under a loupe it looks more like another mineral (something white, not showing crystal form) is growing on the tips of the millerite crystals.
mil-7 ($263.00)Thompson Open Pit, Thompson, Manitoba, Canada
MILLERITE specimen mil-8
$ 60.00
$ 60.00
Dims:5.26x3.78x1.46" (13.4x9.6x3.7cm)
Wt: 1¼lbs (about 560g)
Sarany, Ural Mountain region, Russia
While I am describing this specimen as a millerite specimen, I am torn between several other good descriptions. The millerite is present as several isolated needles, plus a few sparse clusters of needle-like crystals, some of which are curved, and others are branched. The color is a rather metallic green. The next mineral is the largest volume, and is likely just a milky white calcite that has been smoothly etched away to reveal the minerals within. The largest area is a purple mineral sometimes organized in blades or balls (like barite), and sometimes in sprays of acicular crystals, and in some areas appears largely etched away like it might be mangano-calcite and was lost in an acid bath. Then one edge of the host rock looks like it is coated with a purple lepidolite, and finally part of the bottom looks like a silvery mica (perhaps just a very pale lepidolite).
mil-8 ($ 60.00)
Sarany, Ural Mountain region, Russia