Crednerite

Chemical formula: Cu₁+Mn₃+O₂

A rare copper and manganese oxide, forming characteristic black, platy crystals with a metallic luster.

## Characteristics Crednerite is a rare mineral from the oxide group, composed of copper and manganese. It typically occurs as small, thin, tabular or platy crystals, often forming rosette-like or fan-shaped aggregates. Its most distinctive features are its black color and strong, metallic luster on fresh surfaces. Specimens may be covered with coatings of other manganese or copper minerals. ## Physical Properties Crednerite is a relatively soft mineral, with a hardness of about 4.5 on the Mohs scale. It is brittle, and its crystals are easily damaged. It has a high density, approximately 5.46 g/cm³, which is noticeable even in small specimens. It exhibits perfect cleavage in one direction, which accounts for its tendency to form flat, platy shapes. ## Colors and Varieties This mineral is essentially monochromatic. Its color ranges from steel-gray to iron-black. The streak, which is the color of the powdered mineral, is characteristically black. There are no distinct color or commercial varieties. ## History and Name Crednerite was first described in 1850 by Carl Rammelsberg. The mineral is named in honor of the German geologist and mineralogist Hermann Credner (1841–1913). The first specimens came from a mine in Friedrichrode in the Thuringian Forest, Germany. ## Uses Crednerite has no industrial significance. Its occurrence is too rare and in too small quantities. It is solely an object of interest for collectors specializing in rare or systematic minerals.

Properties

Mohs hardness: 4
Color: Bright gray to iron black
Luster: Metallic
Streak: Brownish-black
Density: 4.98
Cleavage: In the plane of the plate; along the striae and inclined about 76° to the plate - less perfect. perfect {001}; also {100}, perfect, <mi>{_111}</mi>, prominent, {111} and {212}, poor.
Fracture: Uneven
Transparency: Opaque
Crystal system: Monoclinic

Diagnostic features

## Identification Crednerite can be identified by its black color, strong metallic luster, perfect cleavage in one direction, and characteristic platy or tabular crystal habit. The black streak is also an important diagnostic feature. ## Distinguishing from Similar Minerals It can be confused with other black, metallic minerals, such as hematite, ilmenite, or some manganese oxides (e.g., hausmannite). It differs from hematite by its black streak (hematite has a reddish-brown streak) and lower hardness. It is distinguished from hausmannite by its more platy habit and perfect cleavage. Identification can be difficult and often requires chemical analysis. ## Crystal Forms Crednerite crystals are typically pseudohexagonal, tabular, or platy, which is a result of crystallization in the monoclinic system. They often form fan-shaped, rosette-like, or radial aggregates. Granular or massive forms are less common.

Geological environment

## Genesis Crednerite is a secondary mineral, forming in the oxidation zones of ore deposits, especially those rich in copper and manganese. It forms under low-temperature conditions as a result of hydrothermal processes or the weathering of primary minerals. ## Mineral Associations It most commonly co-occurs with other manganese oxides, such as hausmannite, pyrolusite, psilomelane, as well as with copper minerals like malachite, azurite, cuprite, and tenorite. Calcite and quartz are also often associated with it. ## Localities The most important localities worldwide include the historical type locality in Friedrichrode (Thuringia, Germany) and the Manganese Mine in Copper Harbor (Michigan, USA). It also occurs in Långban (Sweden), the Atacama Desert (Chile), mines in the Bisbee area (Arizona, USA), and in several locations in Italy and Great Britain (Cornwall).

Rarity

Rare

For collectors

## Quality Criteria The most prized specimens by collectors are those with well-formed, sharp crystals exhibiting a strong luster, forming aesthetic, rosette-like or fan-shaped aggregates. Contrast with the host rock (matrix) on which the crednerite occurs is also important. Specimens from classic, historical localities, such as Friedrichrode or Långban, are particularly sought after. ## Popular Localities Among the most desirable specimens are those from the Manganese Mine in Copper Harbor, Michigan, which are known for their well-formed, lustrous crystals. Historical specimens from Germany and Sweden also fetch high prices due to their scientific significance and rarity.

Care and storage

## Cleaning Due to its softness and perfect cleavage, crednerite requires very careful cleaning. The safest method is to use compressed air to remove dust. If wet cleaning is necessary, use a soft brush and distilled water, then immediately and thoroughly dry the specimen to prevent oxidation. ## What to Avoid Avoid all acids and strong chemicals, which can react with the mineral. Do not use ultrasonic cleaners, which can cause the brittle specimen to disintegrate along cleavage planes. The mineral is stable, but prolonged exposure to moisture can lead to the formation of secondary coatings. ## Storage Crednerite specimens are best stored in separate, padded boxes or on stands to protect them from impacts and scratches. Due to its brittleness, it should not be stored in contact with harder minerals.

External references

https://www.mindat.org/min-1150.html