Maldonite
Chemical formula: Au<sub>2</sub>Bi
Maldonite is a rare, naturally occurring gold-bismuth alloy, characterized by a metallic luster and a color ranging from silvery-white to copper-red.
Properties
- Mohs hardness
- 1.5-2
- Luster
- Metallic
- Streak
- Black
- Density
- 15.46-15.7
- Cleavage
- None
- Fracture
- Sub-Conchoidal
- Transparency
- Opaque
- Crystal system
- Cubic
Diagnostic features
## Identification Key diagnostic features of maldonite include its high density, low hardness, and characteristic pinkish-silver color on a fresh fracture, which quickly tarnishes to black or iridescent. It is malleable and ductile. It often occurs in association with native gold and native bismuth. ## Distinguishing from Similar Minerals It can be confused with native bismuth, which also has a pinkish hue and metallic luster, but bismuth has perfect cleavage, which maldonite lacks. It is distinguished from native gold by its lighter, more silvery color and tendency to tarnish. Other sulfides and sulfosalts are generally harder and more brittle. ## Crystal Forms Maldonite crystals are extremely rare and poorly formed, usually with cubic or octahedral outlines. It is most commonly found as irregular grains, granular aggregates, lamellae, or masses embedded in quartz or other minerals.
Geological environment
## Genesis Maldonite is a hydrothermal mineral. It forms in gold-rich quartz veins, typically under high-temperature conditions. It crystallizes in zones where hydrothermal solutions carrying gold interact with bismuth minerals. ## Mineral Associations It most commonly co-occurs with native gold, native bismuth, bismuthinite, joseite, arsenopyrite, pyrite, chalcopyrite, quartz, and scheelite. ## Localities The most important localities worldwide include the historical type locality in Maldon, Australia. It is also known from other Australian localities in New South Wales and Queensland. Outside Australia, its occurrences have been reported in Bolnäs, Sweden; the Urals, Russia; the Baita Bihor mine, Romania; Little Dalles, Washington (USA); and Atlin and Stewart, British Columbia (Canada), among others.
Rarity
Very rare
For collectors
## Quality Criteria The most valued specimens by collectors are those with well-visible, distinct grains or masses of maldonite, contrasting with light quartz. Associations with crystalline native gold are particularly sought after. The size of the grains and the abundance of occurrence on the rock matrix significantly increase the specimen's value. Iridescent patina is sometimes considered an attractive feature. ## Popular Localities Classic and most desirable specimens come from historical mines in the Maldon region of Australia, which are, however, practically inaccessible. Currently, small quantities of collector material sporadically appear from various localities worldwide, including Canada and Russia.
Care and storage
## Cleaning Maldonite specimens should generally not be cleaned to avoid removing the natural patina, which is often a characteristic feature. If cleaning is absolutely necessary, only compressed air should be used to remove dust. Water and any chemical agents should be avoided. ## What to Avoid Avoid contact with chemicals, acids, and moisture, which can accelerate the oxidation process and damage the specimen. The mineral is very soft and susceptible to scratches. It should not be heated or exposed to sudden temperature changes. ## Storage It is recommended to store maldonite in dry conditions, preferably in a sealed, lidded display box away from other minerals that could scratch it. The use of desiccants should be considered.