Goldamalgam

Chemical formula: (Au,Ag)Hg

Goldamalgam is a naturally occurring alloy (amalgam) of gold, silver, and mercury, forming ductile, silvery-white grains and masses.

## Characteristics Goldamalgam is a natural alloy of mercury with gold and silver, classified as a mercury-rich variety of gold. It occurs as small, irregular grains, nuggets, or ductile masses, rarely forming poorly developed, cubic crystals. Its surface is usually smooth, with a metallic luster, and its color ranges from silvery-white to yellowish, depending on the proportions of gold and silver. Due to the presence of mercury, this mineral is ductile and can be cut with a knife. ## Physical Properties Goldamalgam is characterized by a metallic luster and is opaque. Its hardness on the Mohs scale is 3-3.5, which means it is relatively soft. The density is very high, ranging from 15.47 to 19.3 g/cm³, depending on the chemical composition – the more gold, the higher the density. It is malleable and ductile. ## Colors and Varieties The color of goldamalgam is usually silvery-white, but it can take on shades from white to yellow. The color change is directly related to the ratio of gold to silver content in the alloy. No named commercial or color varieties are distinguished. ## History and Name The name "goldamalgam" comes from its chemical composition – it is an amalgam (an alloy with mercury) of gold. This mineral has been known for a long time, but it was formally described and recognized by the International Mineralogical Association (IMA) in 1982. Historically, natural gold amalgams have been observed in many gold deposits worldwide. ## Uses Goldamalgam is a minor source of gold and silver. Due to its rarity and small accumulations, it is primarily of scientific and collector's interest. It does not have specific industrial applications distinct from gold itself.

Properties

Mohs hardness: 3-3.5
Luster: Metallic
Streak: Silvery-white to yellowish
Density: 15.47 - 19.3
Cleavage: None
Fracture: Malleable
Transparency: Opaque
Crystal system: Cubic

Diagnostic features

## Identification Goldamalgam can be identified by its silvery-white to yellowish color, very high density, metallic luster, and ductility – it can be cut with a knife. It often occurs as irregular grains or coatings on gold. ## Distinguishing from Similar Minerals It can be confused with native gold, silver, platinum, or other amalgams. It differs from gold by its brighter, often silvery color and lower hardness. It is usually denser than silver and may have a yellowish tint. It is distinguished from platinum by its lower hardness. The presence of mercury is a key diagnostic feature, but its confirmation requires chemical analysis. ## Crystal Forms Crystals are extremely rare and poorly developed, taking cubic forms, often with rounded edges. It usually forms irregular grains, flakes, coatings, and massive or spongy aggregates.

Geological environment

## Genesis Goldamalgam forms in the oxidation (weathering) zones of gold deposits, where mercury-containing solutions react with native gold. It forms under low-temperature conditions, close to the Earth's surface. ## Mineral Associations It most commonly co-occurs with native gold, cinnabar (the main source of mercury), quartz, calcite, and other ore minerals found in gold deposits. ## Localities Significant occurrences have been reported in Colombia (Chocó and Nariño departments), Venezuela (Caratal region), Russia (Urals), and the United States (Nevada, California). It also occurs in small quantities in many other gold mining regions worldwide.

Rarity

Rare

For collectors

## Quality Criteria The most prized by collectors are specimens with well-formed, even if small, crystals. Rich aggregates with a distinct, silvery-white color, as well as interesting growths on native gold or quartz, are also highly valued. Due to mercury's toxicity, these specimens are rare on the market and are more of a curiosity for advanced collectors of systematic minerals. ## Popular Localities Localities in Colombia, especially in the Chocó department, are considered classic and provide the best specimens.

Care and storage

## Cleaning Goldamalgam specimens should only be cleaned mechanically, using a soft brush or compressed air to remove dust and loose contaminants. Avoid contact with water and any chemicals. ## What to Avoid The mineral is sensitive to elevated temperatures, which can cause the release of toxic mercury vapors. Absolutely avoid contact with acids and other chemical agents. Due to the presence of mercury, it requires careful handling – it is recommended to wash hands after each contact. ## Storage Specimens should be stored in sealed, airtight containers (e.g., "perky boxes") to prevent mercury evaporation and environmental contamination. Store in a cool, dry, and well-ventilated place, away from direct sunlight and heat sources. Keep it away from other minerals that may react with mercury.

Sources

IMA Mineral List (CNMNC)