THE MINERAL ENARGITE
- Chemistry: Cu3AsS4, Copper Arsenic Sulfide
- Class: Sulfides
- Subclass: Sulfosalts
- Uses: As a minor ore of copper and as mineral specimens.
Specimens
Enargite is related to the rare mineral wurtzite. Wurtzite is a zinc sulfide with a formula of ZnS. In enargite 75% of the zinc atoms are replaced by copper and 25% of the zinc atoms are replaced by arsenic, Cu3AsS4. The similarity is easier to see if wurtzite's formula is rewritten as Zn4S4. The different elements however do not lend themselves to the exact same structure as wurtzite has a symmetry of hexagonal; 6 m m and enargite's symmetry is orthorhombic; 2 m m.
The symmetry of enargite is very uncommon. It belongs to a symmetry class that produced hemimorphic crystals and is typified by the mineral hemimorphite. The hemi means half while the morph means shape. General hemimorphic crystals can have differently shaped tops compared to the bottoms of the crystals. In enargite, the crystals do not have any unique terminations, just a flat face. The "bottom" of the crystals would have a flat face as well, but how do you tell one flat face from another? In the mineral hemimorphite, the top termination faces slant to a point and the bottom termination is much more blunted, a clear difference. Unfortunately for enargite its hemimorphic character is undetectable because of its crystal form.
PHYSICAL CHARACTERISTICS:
- Color is gray to black.
- Luster is metallic.
- Transparency: Crystals are opaque.
- Crystal System is orthorhombic; 2 m m
- Crystal Habits include pseudohexagonal prismatic to blocky or tabular crystals, often terminated by a flat pedion face. Also found massive, granular and in radiating aggregates. Twinning is common and sometimes results in a star shaped cyclic twin called a trilling.
- Cleavage is perfect in two directions, prismatically; distinct in two other directions also prismatically but with different orientations.
- Fracture is uneven.
- Hardness is 3 - 3.5
- Specific Gravity is approximately 4.4+ (average for metallic minerals)
- Streak is black.
- Other Characteristics: crystals are typically striated lengthwise and a tarnish will dull the luster of crystals over time.
- Associated Minerals are
quartz,
bornite,
galena,
sphalerite,
tennantite , chalcocite, chalcopyrite, covellite, pyrite and other sulfides. - Notable Occurrences include Butte, Montana, San Juan Mountains, Colorado and at both Bingham Canyon and Tintic, Utah, USA; Sonora, Mexico; Argentina; Chile; Morococha and Cerro de Pasco, Peru and Island of Luzon, Philippines.
- Best Field Indicators are crystal habit, streak, cleavage and associations.
 Amethyst Galleries' Mineral Gallery MINERALS |
ENARGITE specimen ena-2
$ 22.00
$ 22.00
Dims: 1.6" x 1.4" x 1.3"(4.1 x 3.6 x 3.3 cm)
Wt: 1.68 oz. (47.6 g)
Peru
Though we're unsure of its exact locality, this little Enargite specimen is quite impressive. It consists of a cluster of 4 or 5 prismatic crystals with pedion terminations that have reasonably good form, but show some odd formations in hollows near their bases. The largest of these crystals has dimensions of 0.6 x 0.4 x 0.3" (1.5 x 1.0 x 0.8 cm) and is the only crystal that is not quite complete, as it is missing some material from an area near its base. They have a dark gray coloration, a submetallic, almost adamantine luster, and are opaque. Each are partially coated with a thin skin of what appears to be bornite, as it is very colorful. These crystals rest on a bed of pyrite that includes a few partial pyritohedrons and some unusually long crystalline formations that are actually a type of pseudomorph after Enargite, wherein the pyrite continued to grow over the pseudomorphed crystals. There are also a few thin slivers of white calcite on the pyrite base.
ena-2 ($ 22.00)
Peru
ENARGITE specimen ena-4
$ 47.00
$ 47.00
Dims: 1.5" x 1.4" x 1.1"(3.8 x 3.6 x 2.8 cm)
Wt: 1.98 oz. (56.1 g)
Cerro de Pasco, Peru
This Enargite specimen is one of the most exceptional for its size that I have seen. It consists of at least 5 orthorombic prismatic crystals with pedion terminations intermixed with a few pyrite formations on a bed of broken, intergrown Enargites. The specimen is in generally good condition, with damage limited mostly to larger crystals on the specimen's edge. The largest of these has a noticeably damaged termination, and measures 0.6 x 0.5 x 0.4" (1.5 x 1.3 x 1.0 cm). All of these crystals have a black color, an almost adamantine, submetallic luster, and are opaque. Most are coated with a thin crust of what appears to be bornite, as it is very colorful, with golden, violet, and blue hues. A few other crystals, however, have undergone almost complete pseudomorphing into pyrite, and have a bright metallic luster and a pale golden color. Two of these in particular continued to grow, forming elongated crystal faces and pyritohedral forms. It is a really interesting specimen to examine, as it appears that several stages of the pseudomorphing process are visible at once.
ena-4 ($ 47.00)
Cerro de Pasco, Peru
ENARGITE specimen ena-5
$ 57.00
$ 57.00
Dims: 2.1" x 1.7" x 1.0"(5.3 x 4.3 x 2.5 cm)
Wt: 2.86 oz. (81.2 g)
Peru
One of the most attractive Enargite specimens that I have seen, this particular piece consists of a crust of at least 15 orthorombic prismatic crystals with pedion terminations, mixed with a few pyrite formations. Though there is considerable damage, the specimen is in generally good condition. The largest of these crystals measures about 0.4 x 0.3 x 0.3" (1.0 x 0.8 x 0.7 cm) these crystals have a dark, gray-black coloration, an almost adamantine, submetallic luster, and are opaque. One must look at the broken crystals on the crust's underside in order to see their color and luster, as the intact crystals are almost completely covered by a thin layer of what appears to be bornite, as they are all wonderfully colored with gold and violet hues. They are splendid in appearance! The underside of the specimen shows many broken Enargites mixed with some rather elongated pyritohedrons that are actually covering pseudomorphed Enargites. After they became pyrite, the crystals continued to grow in the pyritohedral form, but were influenced by the original orthorombic crystal shape. I really like this piece- the colors really get to me!
ena-5 ($ 57.00)
Peru
ENARGITE specimen ena-6
$ 77.00
$ 77.00
Dims: 2.4" x 1.7" x 1.5"(6.1 x 4.3 x 3.8 cm)
Wt: 3.39 oz. (96.2 g)
Cerro de Pasco, Peru
There are at least 12 colorful Enargite crystals on the quartzite host rock of this specimen. All show good orthorombic prismatic form with pedion terminations, and only a few that are at the specimen's edge show any damage. The largest of these crystals has a length of only 0.2" (5 mm), but its diameter measures 0.5" (1.3 cm); it rests at an angle to the specimen's base and is partially obscured due to intergrowth. All are opaque, and their gray-black coloration and nearly adamantine submetallic luster are almost completely obscured by a thin layer of what I believe is bornite. This thin layer of material has a metallic luster and shows hints of beautiful violet, gold, and blue coloration. The quartzite base rock on which the Enargites rest is a gray-white in coloration and contains small hollows that are lined with tiny, transparent quartz crystals.
ena-6 ($ 77.00)
Cerro de Pasco, Peru
ENARGITE specimen ena-7
$ 77.00
$ 77.00
Dims: 3.4" x 2.2" x 1.6"(8.6 x 5.6 x 4.1 cm)
Wt: 6.38 oz. (181.0 g)
Peru
This specimen contains at least 10 orthorombic prismatic Enargite crystals on a quartzite base. The crystals are generally in very good condition, though several are slightly damaged and a few on one edge of the specimen are severely so. The largest of these measures 0.4 x 0.4 x 0.3" (1.1 x 1.0 x 0.8 cm), and like the others, has a dark gray-black coloration and a submetallic luster that is nearly adamantine. However,a few of these Enargite crystals are almost completely covered with a thin layer of what appears to be bornite. They have tinges of golden, red-violet, and green colors, and show more of a metallic luster. There is also a substantial amount of pyrite mixed in with the Enargite cluster. Some of these pyrite formations consist of extremely elongated pyritohedrons that are actually coating pyrite pseudomorphs after Enargite. It is a pretty specimen- the golden, metallic pyrite makes a good contrast to the dark color and lustrous shine of the Enargites.
ena-7 ($ 77.00)
Peru
ENARGITE specimen ena-8
$ 100.00
$ 100.00
Dims: 3.0" x 1.7" x 1.5"(7.6 x 4.3 x 3.8 cm)
Wt: 4.70 oz. (133.4 g)
Peru
One of the most interesting specimens that I have come across, this piece's mass is made up mostly of orthorombic Enargite crystals with pedion terminations that rest on a small section of quartzite host rock. Though several of the crystals show considerable and sometimes severe damage, the piece is in generally good condition. The largest of these crystals is quite impressive, with dimensions of 0.5 x 0.4 x 0.4" (1.3 x 1.0 x 1.0 cm), and is in excellent condition. Broken surfaces show their gray-black color, nearly adamantine submetallic luster, and complete opacity. Nearly all of the intact surfaces, however, are covered with a thin layer of what appears to be bornite or a closely-related sulfide. The coating has a more metallic luster than that of the Enargite, and is awash with wonderful golden and red-violet colors. The visible surfaces of the quartzite base on which they rest is at least 50% covered with tiny transparent quartz crystals. It is a very beautiful specimen of an uncommon mineral.
ena-8 ($100.00)
Peru
ENARGITE specimen ena-9
$ 95.00
$ 95.00
Dims: 3.3" x 2.9" x 1.4"(8.4 x 7.4 x 3.6 cm)
Wt: 8.32 oz. (235.9 g)
Cerro de Pasco, Peru
This Enargite specimen is different from most of the others that I have seen in the fact that it occurs in a bladed, rather than prismatic, crystal form with rounded, wedge-shaped terminations. There are at least 20 of these crystals on this specimen, and though nearly half of them are damaged, it is still in relatively good condition. The largest of the intact crystals measures 0.4 x 0.2 x 0.1" (1.0 x 0.5 x 0.2 mm), but several that are broken were considerably larger. The lower halves of their prism lengths are coated with a thin layer of tiny, transparent quartzite crystals. The Enargites have a black color, a surprisingly dull, waxy luster, and are completely opaque. Around these thin blades rest several pyritohedral pyrites of varying size that are in excellent condition and have nearly perfect form. Like the Enargites, they are partially buried by the quartz crystals. All of this rests on a pale gray quartzite host rock.
ena-9 ($ 95.00)
Cerro de Pasco, Peru
ENARGITE specimen ena-10
$ 105.00
$ 105.00
Dims: 2.9" x 2.5" x 2.0"(7.4 x 6.4 x 5.1 cm)
Wt: 13.8 oz. (391 g)
Maria Elana Mine, Chile
The Enargite on this specimen occurs as several large orthorombic prismatic crystals with pedion terminations. There is substantial and obvious damage to the piece, and a few of the crystals are broken and incomplete, but some are intact. the largest of these complete crystals has dimensions of 0.8 x 0.8 x 0.4" (2.0 x 2.0 x 1.0 cm), and like all the others, has a gray-black coloration and a submetallic, almost adamantine luster, and is opaque. They rest on a base made up of intergrown and badly broken pyrite crystals that show a trace of colorful iridescence, and thus likely contain a small amount of bornite.
ena-10 ($105.00)
Maria Elana Mine, Chile
ENARGITE specimen ena-11
$ 30.00
$ 30.00
Dims: 2.0 x 1.7 x 0.9" (5.1 x 4.3 x 2.3 cm)
Wt: 1.13 oz. (32.2 g)
Peru
This small hand specimen consists of a thin quartzite crust on which rest several Enargite crystals. These crystals reach dimensions of 0.4 x 0.4 x 0.2" (1.1 x 1.0 x 0.6 cm) and are in very good condition, showing little fresh damage. Their orthorhombic, pseudo-hexagonal tabular form is moderately good, as its prism edges and faces are not well-defined. All have a deep, nearly black coloration and a bright submetallic luster, but are mostly coated with a thin crust of what appears to be chalcopyrite, given its deep golden coloration, metallic luster, and colorful iridescence. A few pyrite or chalcopyrite crystals are also on hand.
ena-11 ($ 30.00)
Peru
ENARGITE specimen ena-12
$ 36.00
$ 36.00
Dims: 1.0 x 0.9 x 0.8" (2.6 x 2.2 x 1.9 cm)
Wt: 13.0 g
Quirivalca, La Libertad, Peru
A cluster of several small Enargite crystals comprises this specimen. These crystals do not tend to exceed 0.5" (1.3 cm) in length and are generally in good condition, though some are likely cleaved along their basal plane. Their orthorhombic, pseudohexagonal bladed form is very good, and all have a gray-black color and a submetallic luster that is not quite bright enough to be adamantine. Within a few tiny crusts of accompanying calcite lie a few chalcopyrite pseudomorphs after pyrite that have excellent pyritohedral form. There is no host rock, and the piece is hot-glued into a plastic specimen box.
ena-12 ($ 36.00)
Quirivalca, La Libertad, Peru
ENARGITE specimen ena-13
$ 40.00
$ 40.00
Dims: 1.14x0.91x0.51" (2.9x2.3x1.3cm)
Wt: 0.43oz (12.1g)
Butte, Montana, USA
This specimen contains hundreds of enargite crystals on a pyrite base, and there are areas of tiny prismatic quartz crystals present, also. The enargite crystals all have a pseudohexagonal shape with six different sides and a flat termination, and no two crystals look exactly alike. They are black and opaque, and have a metallic luster.
ena-13 ($ 40.00)
Butte, Montana, USA