Tomamaeite

Chemical formula: Cu₃Pt

Tomamaeite is a very rare, naturally occurring copper-platinum alloy, found as fine, metallic grains in sands.

## Characteristics Tomamaeite is a natural alloy (intermetallic compound) of copper and platinum. It occurs as very small, rounded or irregular grains, usually less than 1 mm in size. Its appearance is typically metallic, with a yellowish to reddish-white color, resembling copper or bronze. Due to its extreme rarity and small crystal size, it is a mineral known primarily from scientific research. ## Physical Properties This mineral is opaque and characterized by a metallic luster. Its Mohs hardness is 3.5, placing it in the same category as copper. It is a mineral with a very high density, approximately 12.4 g/cm³, which is a direct result of the presence of the heavy element, platinum. ## Colors and Varieties Tomamaeite has a yellowish to reddish-white color. No varieties of this mineral are distinguished. ## History and Name The mineral's name comes from its discovery location – the coast of Tomamae in Hokkaido Prefecture, Japan. It was first described and approved as a new mineral species by the International Mineralogical Association (IMA) in 2023. Its discovery is a result of research on platinum-group minerals in Japanese placer deposits. ## Uses Tomamaeite has no industrial application due to its extreme rarity. It is solely of scientific importance and is an object of interest for specialized collectors of rare minerals.

Properties

Mohs hardness
3.5
Luster
Metallic
Streak
Cannot be measured.
Density
12.4
Cleavage
None
Fracture
Uneven
Transparency
Opaque
Crystal system
Isometric

Diagnostic features

## Identification Identification of tomamaeite is impossible without advanced analytical techniques. Preliminary identification in heavy mineral concentrates is based on its metallic appearance, reddish hue, and very high density. Definitive identification requires chemical composition analysis, for example, using an electron microprobe (EDS/WDS). ## Distinguishing from Similar Minerals It can be confused with native copper, which has a similar color but significantly lower density. Other platinum-group minerals, such as native platinum, usually have a more silvery-white color. It can only be distinguished from similar alloys, such as tetra-auricupride (CuAu) or hongshiite (CuPt), based on precise chemical analysis. ## Crystal Forms Tomamaeite forms irregular, rounded grains, which is typical for minerals found in placer (alluvial) deposits. Well-formed crystals have not been observed.

Geological environment

## Genesis Tomamaeite is a secondary mineral, found in placer deposits. It forms as a result of erosion and aqueous transport of primary ultramafic rocks (e.g., serpentinites) that contained platinum-group minerals. During transport, heavy and weathering-resistant minerals, including tomamaeite, concentrate in river or coastal sands and gravels. ## Mineral Associations At its type locality in Japan, it co-occurs with other platinum-group minerals, such as native platinum, osmiridium, rutheniridosmine, as well as chromite, magnetite, and native gold. ## Localities The only confirmed and described occurrence of tomamaeite in the world is its type locality – alluvial deposits on the Tomamae coast, in Hokkaido Prefecture, Japan.

Rarity

Extremely rare

For collectors

## Quality Criteria As a microscopic mineral, the main criterion for collector value is the certainty of the specimen's identification, confirmed by a reputable laboratory. The most valuable are grains of the largest possible size, with a distinct color, and specimens where tomamaeite co-occurs with other rare platinum-group minerals. Specimens in host rock (if ever found) would be extremely valuable. ## Popular Localities The only source of specimens is the type locality in Japan. Material from this location is extremely difficult to obtain and is only available within specialized scientific and collecting circles.

Care and storage

## Cleaning Tomamaeite specimens, typically in the form of fine grains in mineral concentrates, do not require cleaning. If they are in the host rock, all mechanical and chemical methods that could damage the delicate grains should be avoided. The safest approach is to leave the specimen in its natural state. ## What to Avoid Avoid contact with acids and other aggressive chemicals that can react with both copper and platinum. Do not subject it to ultrasound or sudden temperature changes. As a metal alloy, it is susceptible to oxidation, so it should be protected from moisture. ## Storage It is recommended to store specimens in a dry environment, preferably in a sealed, lockable 'perky box' or capsule, to limit air and moisture access, which will prevent slow oxidation. It should be protected from dust and mechanical damage.

External references

Sources

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