• Chemistry: Sb2OS2, Antimony Oxysulfide.
  • Class: Sulfides
  • Uses: A very minor ore of antimony and as mineral specimens.
  • Specimens

Kermesite is an unusual sulfide mineral. A close look at the formula can confirm this. There is an oxygen nested between two antimonies and two sulfurs. Kermesite, it turns out, is an intermediate oxidation product between stibnite whose formula is Sb2S3, and various antimony oxides such as senarmontite, Sb2O3; valentinite, also Sb2O3; and stibiconite, Sb3O6(OH). Stibnite when exposed to oxygenated fluids under the right conditions will slowly transform into kermesite as the an oxygen replaces one of the sulfurs in the formula. Usually the oxidation is completed to the point that the sulfurs are completely replaced by oxygen, but in some rare cases the oxidation stops short and forms kermesite. This is fortunate for mineral collectors!

Kermesite is a truly colorful mineral. Its bright red color has been described as a cherry red and that is pretty accurate. The color is caused by the stibnite and is therefore inherent in the mineral. Alternate names or nick-names for kermesite have been used such as red antimony, purple blende and a non-colorful nick-name antimony blende.


  • Color is cherry red to red.
  • Luster is adamantine.
  • Transparency crystals are translucent to rarely transparent.
  • Crystal System is triclinic, bar 1 (pseudo-monoclinic).
  • Crystal Habits include sprays or tufts of aggregated prismatic crystals and as crusts.
  • Cleavage is perfect in one direction.
  • Hardness is 1.0 - 1.5
  • Specific Gravity is approximately 4.5 - 4.8+ (heavy for translucent minerals)
  • Streak is brownish red.
  • Associated Minerals include stibnite and various antimony oxides such as senarmontite, valentinite and stibiconite.
  • Notable Occurrences include Wolfe County, Quebec, Canada; Nova Scotia; Algeria and Sonora, Mexico.
  • Best Field Indicators are color, luster, associations, softness and streak.
KERMESITE specimens:
(hover for more info)
KERMESITE specimen krm-1
$ 120.00
Dims: 2.0" x 1.4" x 1.0" (5.1 x 3.6 x 2.5 cm)
Wt: 3.23 oz. (91.6 g)
Lac Nicolet Antimony Mine, Ham Sud Township, Quebec, Canada
This specimen consists of a small spray of thin, radiating Kermesite needles that rest on a dense, gray, metallic host rock. These needles do not exceed 0.4" (1.0 cm) and appear to be in moderately good condition, though there seems to be a patch of broken crystals that may have made up another spray when they were intact. These needles have a dull, violet-red coloration and show a rather dim adamantine luster due to their compactness, and may be dimly translucent, though that is difficult to determine. Oddly enough, their point of convergence is about 3 mm above the host rock's surface. They rest in a shallow depression in the host rock that is lined with a dull, bright-yellow crust that is very thin. The host rock itself is massive and gray, and shows scores of tiny hollows in which extremely small gray, metallic needles rest. I really don't know what these could be made of, either. Given the sulfur content of the Kermesite, I would be inclined to think that the crust was made of sulfur, and that the tiny needles were made of some sort of antimony sulfide mineral such as stibnite.
no photo
krm-1 ($120.00)
Lac Nicolet Antimony Mine, Ham Sud Township, Quebec, Canada
KERMESITE specimen krm-2
$ 45.00
Dims: 2.7 x 1.8 x 1.2" (6.9 x 4.6 x 3.0 cm)
Wt: 3.69 oz. (104.6 g)
Pezinok, Slovak Republic
Two veins of crystalline Kermesite run through a portion of the dark gray host rock of this specimen. One of these veins is fully exposed, revealing the radiating Kermesite crystals that make it up. They appear to be in good condition, though all are broken and missing their bases and focal points. They do not exceed 0.4" (1.0 cm) in length or 1 mm in diameter. Their thinness makes it difficult to effectively study their triclinic form, but all appear to be reasonably well-formed. Their deep red coloration and adamantine, submetallic luster remind me of cuprite, and all appear to be at least dimly transparent. The host rock in which they rest contains several patches of bright, silvery-gray color and metallic luster, most likely indicating the presence of stibnite.
no photo
krm-2 ($ 45.00)
Pezinok, Slovak Republic
KERMESITE specimen krm-3
$ 40.00
Dims: 3.0 x 2.3 x 1.9" (7.6 x 5.8 x 4.8 cm)
Wt: 4.94 oz. (140.0 g)
Pueta Mine, Tuscany, Italy
Several hollows in the quartz host rock of this specimen are lined with Kermesite, a rather odd antimony oxy-sulfide. The crust shows definite reniform tendencies and coats 2 of the 3 stibnite clusters that are present. The Kermesite has a deep cherry-red coloration, though portions of one crust have a definite gray color and metallic luster. Some of the more exposed areas of the crust are noticeably damaged, but this may be due to natural causes. Besides the stibnite, there are several dozen tiny yellow crystals present that I cannot identify. The host rock is generally made of massive quartz, though all of the hollows within are lined with druses of tiny crystals.
no photo
krm-3 ($ 40.00)
Pueta Mine, Tuscany, Italy
KERMESITE specimen krm-4
$ 65.00
Dims: 7.1 x 4.4 x 1.4" (18.0 x 11.2 x 3.7 cm)
Wt: 2 lbs., 8.1 oz. (1.136 kg)
Pezinok, Slovak Republic
This large cabinet specimen serves as a base rock for 2 small sprays of radiating Kermesite needles. The needles in each spray do not exceed 0.3" (8 mm) in length and are in excellent condition, showing no damage. They are very fine and arranged flush against the surface of the host rock, and so their triclinic form is extremely difficult to study even when using a loupe; however, they appear to be well-formed just from casual study. The needles have the standard deep violet-red coloration and a pearly luster, and are accompanied by many tiny sprays of what is likely stibnite.
no photo
krm-4 ($ 65.00)
Pezinok, Slovak Republic
KERMESITE specimen krm-5
$ 60.00
Dims: 2.2 x 1.6 x 1.4" (5.6 x 4.2 x 3.5 cm)
Wt: 3.0 oz. (86 g)
Pezinok, Czech Republic
At least 4 flat Kermesite sprays rest on the dark gray base rock of this hand specimen. These sprays do not exceed 0.4" (1 cm) in diameter and are generally in very good condition- a small one is somewhat crushed. All show the reddish and/or dark, silvery-gray color and dull metallic luster that are standard for the specie. More of this mineral is barely visible extending from one or two veins in the rock.
no photo
krm-5 ($ 60.00)
Pezinok, Czech Republic
KERMESITE specimen krm-6
$ 105.00
Dims: 1.6 x 1.0 x 0.9" (4.0 x 2.6 x 2.4 cm)
Wt: 1.0 oz. (28 g)
Pezinok, Slovak Republic
This thumbnail piece consists of a chunk of dark gray base rock on which rests a cluster of fine Kermesite needles. These needles are not intergrown with each other, and lay atop the base, as opposed to being embedded into it. All appear to be in good condition, and though they are too thin to effectively study with a loupe, their triclinic form is likely very good. All have the standard deep red color and adamantine luster.
no photo
krm-6 ($105.00)
Pezinok, Slovak Republic
KERMESITE specimen krm-7
$ 60.00
Dims: 2.4 x 1.2 x 1.2" (6.2 x 3.1 x 3.0 cm)
Wt: 3.1 oz. (88 g)
Pezinok, Slovak Republic
A few small clusters of radiating Kermesite needles rest on the gray base of this hand specimen. These crystals do not tend to exceed 3 mm in length, and are very fine. They are in very good condition but are generally either intergrown, embedded into the host, or both, making them difficult to study individually, but they likely have good triclinic form. All have a deep red color and an adamantine luster that is nearly submetallic.
no photo
krm-7 ($ 60.00)
Pezinok, Slovak Republic
KERMESITE specimen krm-8
$ 45.00
Dims: 1.4 x 1.0 x 0.8" (3.5 x 2.5 x 2.0 cm)
Wt: 1.0 oz. (2.8 g)
Pezinok, Slovak Republic
This thumbnail piece consists of an incomplete Kermesite spray that is partly embedded in a gray base rock. The needles that make up the spray are often broken and incomplete, but a few are in good condition, reaching lengths of nearly 0.5" (1.3 cm). They are heavily intergrown with each other and partly embedded, so individual study is nigh impossible. All have a deep red color and an adamantine luster, though a submetallic gray sheen covers them.
no photo
krm-8 ($ 45.00)
Pezinok, Slovak Republic


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