Djurleite
Chemical formula: Cu<sub>31</sub>S<sub>16</sub>
Djurleite is a copper sulfide with a metallic luster, occurring in the enrichment zones of copper deposits, often in association with other sulfides of this metal.
Properties
- Mohs hardness
- 2.5-3
- Luster
- Metallic
- Streak
- Black to grayish-black
- Density
- 5.63
- Cleavage
- Weak/indistinct
- Fracture
- Conchoidal to uneven
- Transparency
- Opaque
- Crystal system
- Monoclinic
Diagnostic features
## Identification Key diagnostic features of djurleite include its black or dark gray color, metallic luster, low hardness (can be scratched by a copper coin), and relatively high density. It is malleable and ductile. It often occurs in compact, massive aggregates. ## Distinguishing from Similar Minerals It can be confused with other copper sulfides, such as chalcocite, digenite, or anilite. Chalcocite is very similar but crystallizes in the monoclinic system (at low temperatures), while djurleite also crystallizes in the monoclinic system but with different symmetry. Precise differentiation of these minerals often requires advanced research methods, such as X-ray diffraction (XRD). It is distinguished from bornite by the absence of the characteristic, variegated iridescence on a fresh fracture. ## Crystal Forms Crystals are rare and usually small, with a short-prismatic or tabular habit. Most often, it forms compact, massive, granular aggregates or occurs as coatings and crusts.
Geological environment
## Genesis Djurleite is a secondary mineral, formed in the supergene (hypogene) enrichment zones of copper ore deposits. It forms as a result of the alteration of primary copper sulfides, such as chalcopyrite or bornite, under conditions of low temperatures and pressures, influenced by sulfur-rich waters. ## Mineral Associations It co-occurs with other copper sulfides, such as chalcocite, digenite, anilite, covellite, as well as bornite, chalcopyrite, tennantite, pyrite, and native copper. ## Localities Important localities worldwide include Tsumeb in Namibia; the Shaba region in the Democratic Republic of Congo; mines in Arizona (e.g., Bisbee), Montana (Butte), and Connecticut in the USA; Mount Isa in Queensland, Australia; and Cornwall in the United Kingdom.
Rarity
Not very common
For collectors
## Quality Criteria The most valued specimens by collectors are those with well-formed, even if small, crystals, which is a great rarity for this mineral. Association with other, more spectacular minerals, forming aesthetic compositions, is also important. In the case of massive aggregates, the value is low, unless the specimen comes from a classic, historical locality. ## Popular Localities Specimens from the Tsumeb Mine in Namibia and the Butte district in Montana, USA, are considered the best. Specimens from these localities are historically and scientifically important.
Care and storage
## Cleaning Djurleite specimens should be cleaned very carefully, preferably dry, using a soft brush. Compressed air can be used to remove dust. Contact with water, especially with added detergents, is not recommended. ## What to Avoid Avoid contact with chemicals, acids, and bases, which can react with sulfides. The mineral is sensitive to moisture and atmospheric oxygen, which can lead to its oxidation and the formation of a dark tarnish. It should not be heated or exposed to sudden temperature changes. ## Storage It is recommended to store specimens in a dry place, preferably in sealed, airtight boxes or display cases, to limit air and moisture access. It is advisable to use desiccants (e.g., silica gel) to ensure stable conditions.