THE MINERAL WILLEMITE
- Chemistry: Zn2SiO4, Zinc Silicate.
- Class: Silicates
- Subclass: Nesosilicates
- Group:
Phenakite - Uses: a minor ore of zinc and as mineral specimens.
Specimens
Dispite being discovered at Franklin first, it was a site in Belgium, where the mineral formed small brown crystals, that gave it its name, willemite. It seems that the minerologists at Franklin described the mineral but never named it. In the meantime the minerologists at Belgium named the mineral after William I of Belgium.
Willemite is one of the few silicate minerals that have a trigonal symmetry. This symmetry is far more common among carbonates than among silicates. Willemite shares the same symmetry with the emerald green silicate dioptase and the closely related silicate phenakite. Although massive willemite is much more common, some crystals do show the rhombohedral terminations atop hexagonal prisms that is characteristic of it symmetry.
Willemite's great desirability is not so much its use as a zinc ore, its rarity, its associations or even its crystal habits as it is its wonderful fluorescence. Nearly all willemite specimens fluoresce a bright green under ultra-violet light. This fluorescence combined with the red fluorescence of the calcite at Franklin, makes specimens from there even more special. Some willemite specimens will even show phosphorescence. Phosphorescence is the ability of a mineral to glow after the initial light is removed. The mineral has essentially stored the energy of the initial activating light and re-emits light on a delayed basis. Willemite is one of the best examples of a fluorescent mineral and is a must have for any collector interested in this phenomenon.
PHYSICAL CHARACTERISTICS:
- Color is usually colorless or white but can be tinted yellow, blue, red, brown and often green.
- Luster is vitreous to resinous.
- Transparency crystals are transparent to translucent.
- Crystal System: trigonal; bar 3
- Crystal Habits include typically short prismatic crystals although some prismatic crystals can be rather long with sometimes very steep rhombohedral terminations. Also as granular, lamellar and fibrous masses.
- Cleavage in good in one direction (basal)
- Fracture is conchoidal to uneven.
- Hardness is 5.5
- Specific Gravity is approximately 3.9 - 4.2 (above average for non-metallic minerals).
- Streak is white.
- Other Characteristics: strongly fluorescent green and sometimes phosphorescent.
- Associated Minerals are zincite, franklinite, rhodonite, calcite,
greenockite and other rare minerals. - Notable Occurrences include of course Franklin as well as Paterson and Sterling Hill, New Jersey and Mammoth Mine, Tiger, Arizona, USA; Morsnet, Belgium; St. Hilaire, Quebec; Tsumeb, Namibia and Greenland.
- Best Field Indicators are fluorescence, associations, luster, cleavage and crystal habit.
 Amethyst Galleries' Mineral Gallery MINERALS |
WILLEMITE specimen wil-1
$ 48.00
$ 48.00
Dims: 2.0" x 1.9" x 0.8" (5.1 x 4.8 x 2.0 cm)
Wt: 2.92 oz. (82.9 g)
Franklin, New Jersey, U.S.A.
I have seen many Willemite specimens in my travel, but none with as bright a green color as this one! The Willemite occurs as very small (2-3 mm maximum diameter), rounded crystals in a matrix of white calcite, along with equally small, rounded franklinite crystals. They have a pale yellow-green color and a pearly luster, and are translucent and possibly transparent. Exposure to shortwave UV radiation causes the Willemite to glow green with an almost unparalleled brightness that dims the already dull red glow of the calcite. I was very impressed with this specimen, as most of the other available Willemite pieces were a dirty, yellow-brown color.
wil-1 ($ 48.00)
Franklin, New Jersey, U.S.A.
WILLEMITE specimen wil-2
$ 90.00
$ 90.00
Dims: 5.0 x 3.4 x 1.0" (12.7 x 8.6 x 2.5 cm)
Wt: 11.3 oz. (319 g)
Sussex County, New Jersey, U.S.A.
This large hand specimen consists of a slab of calcite matrix rock through which runs a thick vein of massive Willemite. The Willemite shows no crystal form and has dull, uneven surfaces. Its color is a very pale green-yellow, and it is completely opaque and not especially easy to discern from the surrounding host material. However, when bathed in shortwave UV radiation, it is easy to see because of its bright green fluorescence (see the second image). The calcite host glows only a very dull red color under bright shortwave UV light, and contains perhaps hundreds of tiny franklinite crystals that are easy to see due to their black coloration.
wil-2 ($ 90.00)
Sussex County, New Jersey, U.S.A.
WILLEMITE specimen wil-3
$ 90.00
$ 90.00
Dims: 4.6 x 2.4 x 1.7" (11.7 x 6.1 x 4.3 cm)
Wt: 1 lb., 1.7 oz. (503 g)
Sussex County, New Jersey, U.S.A.
This specimen consists of a large, formless chunk of massive Willemite that is partly suffused with a few other minerals. There may also be several definite Willemite crystals present, but if so, all of them are broken. The Willemite has a green-yellow coloration (though some of the material has a reddish hue) and a dull luster, and is basically opaque. Trapped within this material are hundreds of tiny franklinite crystals- all of the exposed crystals are broken, and many are otherwise warped due to growing conditions or intergrowth. There is also a small amount of calcite present.
wil-3 ($ 90.00)
Sussex County, New Jersey, U.S.A.
WILLEMITE specimen wil-4
$ 100.00
$ 100.00
Dims: 2.4 x 2.2 x 1.0" (6.1 x 5.6 x 2.5 cm)
Wt: 3.73 oz. (105.9 g)
Tsumeb Mine, Tsumeb, Namibia
A cluster of several small Willemite crystals rests on the smithsonite host rock of this specimen. These crystals are well-protected but almost impossible to effectively study due to the fact that they are covered with a crust of crystalline smithsonite. Under powerful shortwave UV light, one can see the dull green glow of the Willemites beneath the nonreactive smithsonite layer. The smithsonite itself has good trigonal prismatic form and occurs as small (0.2 or 5 mm max. length) prisms with hexagonal cross-sections. The host material is made up of both crystalline and botryoidal smithsonite, and there is likely some calcite present, as parts glow with an orange color under the UV light.
wil-4 ($100.00)
Tsumeb Mine, Tsumeb, Namibia
WILLEMITE specimen wil-5
$ 65.00
$ 65.00
Dims: 5.2 x 2.7 x 2.9" (13.2 x 6.9 x 7.2 cm)
Wt: 1 lb., 9.9 oz. (734 g)
Sterling Hill Mine, Ogdensburg, New Jersey, U.S.A.
Though it is very difficult to see under white light, this cabinet specimen contains a sizable amount of Willemite. When exposed to shortwave UV light, the classic bright-green fluorescent color of the Willemite is very easy to see. It appears to show no crystal form, and its dark brown color blends in with the dark color of the biotite mica that covers most of the piece. A substantial amount of massive, white calcite is also present- it exhibits a rather bright orange fluorescent color under UV.
wil-5 ($ 65.00)
Sterling Hill Mine, Ogdensburg, New Jersey, U.S.A.
WILLEMITE specimen wil-6
$ 45.00
$ 45.00
Dims: 4.3 x 3.8 x 2.2" (10.8 x 9.6 x 5.6 cm)
Wt: 1 lb., 2.7 oz. (529 g)
Sterling Hill Mine, Ogdensburg, New Jersey, U.S.A.
Several chunks of seemingly massive Willemite are embedded in the calcite matrix of this display piece. These pieces show no crystal form and only irregular breakage surfaces. Their color is a dull brown, their luster is dull and waxy at best, and they are completely opaque. However, when exposed to shortwave ultraviolet light, all glow with the classic bright green color of their specie, which contrasts magnificently with the bright orange glow of the surrounding calcite. Small bits of franklinite and large pieces of another mineral accompany the Willemite- I think that they are made of rhodonite, though zincite is a remote possibility.
wil-6 ($ 45.00)
Sterling Hill Mine, Ogdensburg, New Jersey, U.S.A.
WILLEMITE specimen wil-7
$ 68.00
$ 68.00
Dims: 2.1 x 1.6 x 1.2" (5.3 x 4.1 x 3.0 cm)
Wt: 2.86 oz. (81.2 g)
Trotter's Dump, Franklin, New Jersey, U.S.A.
This hand specimen consists of 3 or 4 partial Willemite crystals. The largest of these has dimensions of 1.1 x 1.0 x 0.7" (2.7 x 2.4 x 1.7 cm) and is the most complete, though its termination is broken off. It shows excellent trigonal prismatic form where intact, however, and has a good hexagonal cross-section. All have a moderate pink-brown coloration and a dull, waxy luster- however, when bathed in shortwave ultraviolet light, they glow a very bright green. The Willemites are accompanied by several black franklinite octahedrons, some of which are embedded in the Willemites themselves, and all rest in a matrix of white calcite. The calcite glows a moderate orange-red coloration under ultraviolet light, and the franklinites are inert and do not glow.
wil-7 ($ 68.00)
Trotter's Dump, Franklin, New Jersey, U.S.A.
WILLEMITE specimen wil-8
$ 30.00
$ 30.00
Dims: 3.6 x 3.4 x 2.6" (9.2 x 8.5 x 6.6 cm)
Wt: 1 lb., 8.9 oz. (706 g)
Franklin, New Jersey, U.S.A.
This large cabinet specimen consists of a chunk of dull white calcite matrix in which rest a layer and countless grains of Willemite. There is no evidence of crystal form in any of the material, and the Willemite is difficult to see against the pale calcite background. When held under a shortwave ultraviolet light, however, one can easily see the bright green glow that is characteristic of this mineral against the bright orange glow of the calcite. A large number of black franklinite nodules are also present- these do not glow under u/v light. The red-brown Willemite band in the rock is easier to see, however, and also fluoresces green.
wil-8 ($ 30.00)
Franklin, New Jersey, U.S.A.
WILLEMITE specimen wil-14
$ 100.00
$ 100.00
Dims: 4.29x3.31x3.27" (10.9x8.4x8.3cm)
Wt: 3 lbs (1 kg)
Sterling Hill, Ogdensburg, New Jersey, USA
This large specimen is a classic Franklin/Sterling Hill specimen, as it contains a significant fraction of each of the 4 major minerals found there. One end is nearly covered with franklinite crystals, there are several large zincites, and (under a short-wave UV lamp) the bright orange glow of calcite, and the bright green glow of willemite are apparent. The fluorescent image does not look nearly as good as the specimen appears to the human eye. One face of the specimen shows all four minerals well. As is normal with Franklin specimens, there are no natural crystal surfaces exposed, and it looks rather dirty. Under a loupe, the zincite appears translucent and deep red, and good cleavage surfaces show on some of the franklenites.
wil-14 ($100.00)
Sterling Hill, Ogdensburg, New Jersey, USA
WILLEMITE specimen wil-10
$ 29.00
$ 29.00
Dims: 2.85x2.38x2.11" (7.25x6.04x5.37cm)
Wt: 8.85oz (250.4g)
Franklin, New Jersey, USA
This is a granular mass of pale green willemite, black franklinite, and red zincite crystals. It contains about 50% willemite, 40% franklinite, and 10% or less of zincite. Under a UV lamp, the willemite glows an intense green, making this an excellent fluorescent specimen. The image was taken under a short-wave ultraviolet lamp.
wil-10 ($ 29.00)
Franklin, New Jersey, USA
WILLEMITE specimen wil-11
$ 29.00
$ 29.00
Dims: 2.46x2.44x1.80" (6.26x6.20x4.58cm)
Wt: 18.62oz (528g)
Franklin, New Jersey, USA
A classic Franklin specimen, this is mostly franklinite by weight, followed by light gray willemite, and also there is a significant number of small red zincite crystals. All three minerals are in the form of small crystals - none are very large, and none are well-formed. Under long-wave UV, the willemite glows a brilliant green.
wil-11 ($ 29.00)
Franklin, New Jersey, USA