Omariniite

Chemical formula: Cu₁+₈Fe₃+₂Zn₂+Ge₄+₂S₂-₁₂

Omariniite is a rare copper, iron, zinc, and germanium sulfide, discovered in Argentina, forming metallic grains in association with other germanium minerals.

## Characteristics Omariniite is a very rare sulfide mineral, first described in 2016. It occurs as very fine, anhedral (lacking crystal faces) grains, usually not exceeding 100 micrometers in size. These grains are most often intergrown with other minerals, mainly galena. It is opaque and has a metallic luster. ## Physical Properties Due to the small size of the grains, many physical properties of omariniite have not been fully determined. Its Mohs hardness is estimated to be 4 to 4.5. The mineral exhibits a metallic luster and is opaque. Its streak is black. The density calculated from the chemical formula and unit cell parameters is 4.75 g/cm³. ## Colors and Varieties Under reflected light microscopy, omariniite appears gray with a slight creamy tint. No internal reflections have been observed. No varieties of this mineral have been distinguished. ## History and Name The mineral was discovered in the Pingüino polymetallic deposit in Santa Cruz Province, Argentina. It was approved by the International Mineralogical Association (IMA) in 2015 under the number IMA2015-059. The name honors Dr. Omar Ricardo Omarini (1946–2012), an Argentine geologist who made significant contributions to the geological research of northwestern Argentina, including the region where the discovery was made. ## Uses Omariniite has no industrial or commercial applications. Its significance is purely scientific and as a collector's item, being a very rare germanium-bearing mineral.

Properties

Mohs hardness: 4-4.5
Luster: Metallic
Streak: Black
Density: 4.75
Transparency: Opaque
Crystal system: Tetragonal

Diagnostic features

## Identification Identification of omariniite is impossible without advanced laboratory techniques. It requires analysis under reflected light using a metallographic microscope and confirmation of its chemical composition using an electron microprobe (EDS/WDS) or X-ray diffraction (XRD). In reflected light, it is gray with a creamy tint, non-pleochroic, and weakly anisotropic. ## Distinguishing from Similar Minerals Omariniite is very similar to other germanium sulfides, such as briartite, germanite, and putzite. It occurs in intimate intergrowth with them. Distinguishing it from these minerals requires precise chemical analysis, as they have similar optical properties. Compared to germanite, omariniite is slightly brighter. ## Crystal Forms This mineral forms exclusively anhedral, irregular grains, often with rounded or amoeboid shapes. It has not been observed in the form of well-developed crystals. These grains occur as inclusions or in intergrowths with other sulfides.

Geological environment

## Genesis Omariniite forms as a result of hydrothermal processes in polymetallic veins. In its only known locality (the Pingüino deposit), it is associated with low-sulfidation vein mineralization, formed under epithermal conditions. It crystallized from hydrothermal solutions rich in copper, iron, zinc, germanium, and sulfur. ## Mineral Associations This mineral occurs in close association with other rare germanium minerals. It most commonly co-occurs with putzite, germanite, briartite, galena, sphalerite, chalcopyrite, and pyrite. Its grains are typically intergrown with galena or form intergrowths with putzite and germanite. ## Localities The only confirmed locality for omariniite in the world is its type locality – the Pingüino deposit, located in the Deseado Department, Santa Cruz Province, Argentina.

Rarity

Extremely rare

For collectors

## Quality Criteria As a microscopic mineral, omariniite is not evaluated by typical criteria such as size or crystal form. The collector's value of a specimen depends on the confirmed presence of the mineral through analysis and on the richness and diversity of associated rare germanium minerals (putzite, germanite) on the same fragment. The most valuable are polished sections where omariniite grains can be identified and photographed under a microscope. ## Popular Localities The only source of specimens is the Pingüino deposit in Argentina. Material from this locality is extremely difficult to acquire and primarily goes to research institutions and specialized systematic collections.

Care and storage

## Cleaning Due to its extreme rarity and microscopic grain sizes intergrown with other minerals, specimens containing omariniite should not be cleaned mechanically or chemically. Any attempt to isolate or clean them risks irreversible destruction of the mineral. ## What to Avoid Avoid all chemicals, ultrasonics, temperature changes, and attempts to polish or grind the rock matrix. Specimens should be protected from dust and chemical air pollutants. ## Storage Specimens containing omariniite, typically in the form of polished sections for microscopic examination or small fragments of the host rock, should be stored under stable conditions, in specialized "micromount" boxes or sealed containers, to protect them from dust and mechanical damage.

Sources

IMA Mineral List (CNMNC)