Donpeacorite
Chemical formula: Mn<sup>2+</sup>MgSi<sub>2</sub>O<sub>6</sub>
Donpeacorite is a rare pyroxene group mineral, a magnesium-manganese silicate characterized by its brown color.
Description
## Characteristics Donpeacorite is a member of the pyroxene group and belongs to the orthopyroxene series. It is the manganese analogue of enstatite. It typically forms prismatic, elongated crystals or occurs as granular aggregates and rock masses. Its appearance is typical of pyroxenes, although it is distinguished by a characteristic, often intense brown or reddish-brown color, resulting from the presence of manganese. ## Physical Properties This mineral is characterized by a hardness of approximately 6 on the Mohs scale, which is typical for silicates in this group. It has a vitreous luster, and its transparency ranges from translucent in thin fragments to almost opaque in larger pieces. The density of donpeacorite is approximately 3.48 g/cm³. ## Colors and Varieties Donpeacorite occurs in shades of brown, from light brown to deep reddish-brown. Its color is one of its key visual features. There are no known commercial or colored varieties. ## History and Name The mineral's name, approved in 1984, honors Donald R. Peacor (1932–2011), a professor of mineralogy at the University of Michigan in the USA, in recognition of his contributions to the study of rock-forming minerals, including pyroxenes. It was discovered and described based on material from the Bald Knob deposit in North Carolina, USA. ## Applications Due to its rarity, donpeacorite has no industrial applications. It is solely an object of scientific interest and a valued acquisition for advanced systematic mineral collections.
Diagnostic features
## Identification Donpeacorite can be preliminarily identified by its brown or reddish-brown color, prismatic crystal habit, hardness of approximately 6, and occurrence in manganese-rich metamorphic rocks. Its characteristic cleavage, typical of orthopyroxenes, is also distinctive. ## Differentiation from Similar Minerals It can be confused with other pyroxenes, such as enstatite (usually lighter, if iron-free) or ferrosilite. Rhodochrosite (which is much softer and reacts with acids) and rhodonite (which crystallizes in a different system and has different cleavage) can also be similar in appearance and environment of occurrence. Definitive identification almost always requires chemical analysis (e.g., EDS) or X-ray diffraction (XRD) studies. ## Crystal Forms Donpeacorite crystals have a prismatic habit, often columnar and elongated. It also occurs as granular, fibrous aggregates or as massive aggregates embedded in rock.
Geological environment
## Genesis Donpeacorite is a mineral typical of metamorphic rocks that have undergone metamorphism under conditions of high temperatures and pressures. It forms as a result of the transformation of manganese- and silica-rich sediments, such as manganiferous cherts. ## Mineral Associations It often co-occurs with other manganese minerals, forming characteristic parageneses. The most common associated minerals include rhodonite, spessartine (manganese garnet), tephroite, galaxite, bustamite, and manganese oxides. ## Localities The most important and type locality is the Bald Knob deposit in Alleghany County, North Carolina, USA. Significant specimens also come from the Broken Hill deposit in New South Wales, Australia. The mineral has also been reported in several localities in Japan (e.g., Noda-Tamagawa mine) and Sweden (Långban).
Rarity
Very rare
Collector aspects
## Quality Criteria The most prized by collectors are well-formed, sharply terminated crystals with an intense, reddish-brown color. Specimens in which donpeacorite crystals are embedded in a mineralogically contrasting matrix or co-occur with other rare manganese minerals are highly valued. Crystal size is also important, as larger specimens are exceptionally rare. ## Popular Localities Specimens from the type locality, Bald Knob in the USA, are considered classic and most desirable. Rich aggregates from Broken Hill in Australia, which often contain parageneses with other rare minerals, are also very popular.
Care and storage
## Cleaning Donpeacorite specimens should be cleaned gently, using a soft brush and distilled water. Ultrasonic cleaners should be avoided, as they can cause fractures along cleavage planes. ## What to Avoid The mineral is sensitive to strong acids. Despite its relatively high hardness, it is brittle, so it should be protected from impacts and falls. Sudden temperature changes should also be avoided. ## Storage It is recommended to store specimens in separate, padded boxes or display cases to prevent scratches from harder minerals. Exposure to strong, direct sunlight is not advisable, although there is no evidence of particular photosensitivity.