Shagamite

Chemical formula: KFe<sup>3+</sup><sub>11</sub>O<sub>17</sub>

Shagamite is an extremely rare potassium iron oxide, found only in one location worldwide as microscopic inclusions.

## Characteristics Shagamite is a mineral from the oxide group, described as microscopic, hexagonal or pseudohexagonal lamellae not exceeding 100 micrometers in size. It occurs as inclusions within other minerals, mainly enstatite. Its appearance in reflected light is gray, with internal reddish-brown reflections. ## Physical Properties Due to the microscopic size of the crystals, most physical properties, such as hardness, density, or luster, have not been precisely determined. The mineral is opaque. ## History and Name The name Shagamite comes from its discovery location in the Shagam intrusion in Venezuela. The mineral was approved by the International Mineralogical Association (IMA) in 1981 (IMA1981-017). It was described by J.W. Reid, G.J. Gac, and others in a 1983 publication.

Properties

Transparency
Opaque
Crystal system
Hexagonal

Diagnostic features

## Identification Identification of shagamite is possible only through advanced laboratory techniques, such as electron microscopy (SEM) combined with chemical composition analysis (EDS) or electron microprobe analysis (EMPA). In reflected light under a polarizing microscope, it exhibits weak pleochroism from gray to grayish-brown. ## Distinguishing from Similar Minerals Due to its unique chemical composition and occurrence, it is difficult to confuse with other minerals after chemical analysis. Visually, without analysis, it is impossible to distinguish from other microscopic, opaque inclusions. ## Crystal Forms It forms small, hexagonal or pseudohexagonal lamellae and plates, typically less than 100 micrometers in size.

Geological environment

## Genesis Shagamite forms under conditions of high-temperature contact metamorphism. At its type locality, it was found in anorthositic gabbros that were affected by a tonalitic intrusion. It is believed to have formed as a result of reactions between primary minerals at very high temperatures. ## Mineral Associations This mineral coexists with enstatite (in which it forms inclusions), ilmenite, magnetite, plagioclase (labradorite), hercynite, and corundum. ## Localities The only confirmed occurrence of shagamite worldwide is its type locality – the Shagam intrusion in Lara State, Venezuela.

Rarity

Extremely rare

For collectors

## Quality Criteria Shagamite does not appear on the collector's market as a standalone mineral. The only value for collectors and scientific institutions are rock specimens from the type locality where the presence of this mineral has been confirmed. The value is purely scientific and depends on the quality of documentation and analyses confirming the presence of shagamite.

Care and storage

## Cleaning Due to its extreme rarity and microscopic nature of occurrence (as inclusions in the host rock), individual crystals are not isolated. Cleaning applies only to the entire matrix specimen and should be limited to gently removing dust with a soft brush. ## What to Avoid Avoid all chemical, ultrasonic, and mechanical cleaning methods that could damage the host rock and the inclusions themselves. Protect from acids and strong bases. ## Storage Specimens containing shagamite should be stored in stable conditions, away from moisture, dust, and direct sunlight, preferably in a sealed collector's box.

Sources

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