Guidottiite

Chemical formula: Mn²⁺₂Fe³⁺(SiFe³⁺)O₅(OH)₄

Guidottiite is a rare, brown mineral from the serpentine group, being a manganese and iron analog of cronstedtite.

## Characteristics Guidottiite is a mineral from the serpentine group, closely related to cronstedtite. It occurs as very fine, hexagonal plates that form rosette-like or spherical aggregates up to 0.2 mm in size. Its structure and chemical composition make it a manganese-iron analog of cronstedtite. Due to the microscopic size of the crystals, its visual features are difficult to observe without specialized equipment. ## Physical Properties Guidottiite crystals exhibit a luster described as vitreous to dull. Hardness and density have not been precisely measured due to the small size and nature of the aggregates, but are estimated based on analogy with other minerals from the serpentine group. ## Colors and Varieties This mineral has a characteristic brown color. No varieties have been distinguished. ## History and Name Guidottiite was discovered in material from the Woods Creek mine in Fresno County, California (USA). It was approved as a new mineral by the International Mineralogical Association (IMA) in 2009 (IMA2009-035). The name honors Professor Charles V. Guidotti (1935–2005) of the University of Maine, in recognition of his contributions to the study of serpentine group minerals and micas. ## Uses Guidottiite has no industrial application and is of purely scientific and collecting interest for specialists collecting rare minerals or microminerals.

Properties

Mohs hardness
4-4.5
Color
Black
Luster
Vitreous to Dull
Streak
Brown
Density
3.33
Cleavage
(001)
Fracture
Micaceous
Transparency
Opaque
Crystal system
Hexagonal

Diagnostic features

## Identification Identification of guidottiite is possible only through advanced analytical methods, such as X-ray diffraction (XRD) and chemical analysis (e.g., electron microprobe). Visual identification in the field or in a collection is impossible due to its microscopic size and resemblance to other serpentine minerals, such as cronstedtite. ## Distinguishing from Similar Minerals Guidottiite is visually indistinguishable from cronstedtite and other fine-grained, dark minerals from the serpentine group. The key distinguishing feature is the dominance of manganese (Mn²⁺) over iron (Fe²⁺) in a specific structural position, which can only be determined by chemical analysis. ## Crystal Forms Guidottiite forms microscopic, hexagonal, thin plates. These plates aggregate into rosette-like, spherical, or hemispherical forms.

Geological environment

## Genesis Guidottiite forms as a result of hydrothermal processes in ultramafic rocks, such as serpentinites. It forms in veins cutting serpentinite, likely under low-temperature conditions. ## Mineral Associations This mineral co-occurs with other minerals from the serpentine group, such as lizardite and cronstedtite. In the type locality (Woods Creek mine), it was found in association with lizardite. ## Localities The only confirmed and described locality of guidottiite worldwide is its discovery site - the Woods Creek mine in Fresno County, California, USA. This is an abandoned chromite mine.

Rarity

Very rare

For collectors

## Quality Criteria As a micromineral, guidottiite is primarily valued for the mere fact of its confirmed presence in a collection. The most highly rated specimens are those on which well-formed, though microscopic, spherical or rosette-like aggregates are visible, clearly standing out from the host rock (matrix). Precise documentation confirming the mineral's identification is also important. ## Popular Localities The only source of guidottiite specimens is its type locality: the Woods Creek mine in California, USA. All specimens available on the collector's market come from this single location.

Care and storage

## Cleaning Specimens should be handled with the utmost care. Due to the microscopic size and delicacy of the aggregates, mechanical cleaning is not recommended. If absolutely necessary, compressed air (from a safe distance) can be used to remove dust. Avoid contact with water and chemicals. ## What to Avoid Avoid all chemicals, especially acids, which can destroy the mineral. The aggregates are very brittle and sensitive to shocks and touch. Do not expose specimens to high temperatures or humidity. ## Storage Guidottiite specimens, typically microminerals, should be stored in specialized "micromount" boxes that protect them from mechanical damage, dust, and humidity. Avoid vibrations and shocks.

External references

Sources

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