How do I identify Guyanaite?

Guyanaite can be identified by its Reddish brown color. Look for these key characteristics when examining specimens.

What color is Guyanaite?

Guyanaite typically appears in Reddish brown, golden brown, greenish brown, green,. Color can vary depending on impurities and formation conditions.

Guyanaite

A variety of Minerals

What is Guyanaite?

Guyanaite (CrOOH) is a chromium oxide mineral that forms as an intergrowth with other chromium oxide minerals known as bracewellite (CrOOH) and grimaldiite (CrOOH) as well as eskolaite (Cr2O3) which in early findings were nearly indistinguishable from one another. These oxides formed so closely as intergrowths with one another that they were initially, and erroneously, identified as a single definite mineral previously known as merumite. Because of its complex history and the previously undiscovered nature of these chromium oxide polymorphs, the relevance of any information found in many early experiments involving the mineral formerly known as merumite in regard to guyanaite is unknown and it is implied that in any further reference of merumite it will have been composed of a mineral assemblage including guyanaite. The rare occurrence and complexity from intergrowth of naturally occurring guyanaite hinders experimental work, leading to laboratory synthesized samples which help to better experiment with the minerals.

Guyanaite Market Value Calculator

Estimate the market value of Guyanaite using size, quality, and finish. This preview calculator is for quick context and is not a formal appraisal.

Guyanaite Localities Map

See where Guyanaite is found with a localities map, collecting zones, and geology context. Generate a sample map preview below.

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North ZoneCentral RidgeSouth Basin

Key Characteristics

Characteristics of Guyanaite

Because of the high level of difficulty in obtaining a pure mineral sample of guyanaite, experimentation is carried out on samples of a known complex composition which is determined by x-ray and optical studies. The complex intergrowth of chromium oxide minerals results in poor samples for analyzing physical properties such as hardness, measured density, cleavage, habit, and luster giving incomplete data and an inability to determine values for each. A number of “merumite” grains shown to be almost entirely guyanaite by means of x-ray diffraction do however have a yellow-brown streak. The other known physical properties vary greatly based on which one of the two major locations this mineral is found. Samples from Guyana are distinguished by the brown, red, and sometimes green color of prismatic crystals as much as .1 mm long and a light-green to greenish-black variety is occasionally found forming in prismatic microcrystalline aggregates where samples from the Otokumpu mine in Finland occur as aggregates of golden-brown to greenish-brown fibers which replace smaller crystals of eskolaite that are less than 1.0 mm in size.

Composition of Guyanaite

Guyanaite has a chemical formula of CrO(OH), it was first identified primarily by means of X-ray powder diffraction and chemical data and has been confirmed in recent studies by means of X-ray diffraction, optical reflectance, and infrared absorption (IR) spectroscopy. It is both trimorphous with, and shares an exact chemical formula with both bracewellite and grimaldiite which are also chromium oxides, differing only in their mineralogical structure being orthorhombic with space group Pnnm, orthorhombic with space group Pbnm, and hexagonal with space group R3m, respectively. It is formed from the parent compound of CrO2 by means of one of two processes. The first process for the conversion of CrO2 into CrOOH occurs through a reduction of CrO2 in the presence of H2O and a reductant (oxalic acid or steel) resulting in the chemical equation of (2CrO2 + H2O → 2CrO(OH) + ⁄2O2). The second process is an oxidation of the chromium ion using a solution as a solvent. Such a reaction is represented by the chemical equation (3CrO2 + 2NaOH → Na2CrO4 + 2CrO(OH)).