Stumpflite

Chemical formula: PtSb

Stumpflite is a rare mineral from the antimonide group, composed of platinum and antimony, forming tiny, metallic inclusions in other minerals.

## Characteristics Stumpflite is a rare mineral from the sulfide class, more specifically a platinum antimonide. It occurs as very small, rounded or irregular grains, usually as inclusions in other minerals, mainly stibiopalladinite. Its maximum observed size is about 1x1 mm. It is opaque and has a metallic luster. In reflected light, its color is white with a slight creamy tint. ## Physical Properties Due to the small size of the grains, many physical properties have not been precisely determined. Hardness on the Mohs scale is estimated at about 5. The mineral is characterized by high density, 11.89 g/cm³, which is typical for platinum-bearing minerals. It has a metallic luster and is opaque. ## Colors and Varieties Stumpflite has a steel-gray to tin-white color. In reflected light under a polarizing microscope, it shows a creamy-white color. No varieties are known. ## History and Name The mineral was first described in 1972 by Z. Johan and P. Picot. The name honors Eugen Friedrich Stumpfl (1931–2004), an Austrian mineralogist and professor at the University of Leoben in Austria, for his contributions to the study of platinum group minerals. Type specimens come from the Driekop deposit in South Africa. ## Uses Stumpflite has no industrial application. It is of purely scientific and collecting interest as a rare platinum mineral.

Properties

Mohs hardness: 5
Color: Creamy-white
Luster: Metallic
Streak: Black
Density: 0
Cleavage: None
Fracture: Uneven
Transparency: Opaque
Crystal system: Hexagonal

Diagnostic features

## Identification Identification of stumpflite is extremely difficult without specialized equipment. Due to its occurrence as microscopic grains, it requires analysis in reflected light (polarizing microscope) and chemical methods, such as X-ray microanalysis (EDS/WDS). Its key features include high reflectivity, creamy-white color, and co-occurrence with other platinum group minerals. ## Distinguishing from Similar Minerals It can be confused with other antimonides and platinum group metal alloys, such as genkinite, stibiopalladinite, or geversite. Differentiation is possible almost exclusively based on chemical composition analysis. In reflected light, stumpflite is brighter than co-occurring geversite. ## Crystal Forms Stumpflite crystals have not been observed. This mineral forms only very small, irregular or rounded grains and anhedral (xenomorphic) aggregates, usually less than 1 mm in size.

Geological environment

## Genesis Stumpflite is a mineral of magmatic origin. It forms in ultramafic and mafic layered intrusions, in zones rich in chromite and sulfides. It crystallizes in the late stages of magmatic processes, often in association with other platinum group minerals. ## Mineral Associations This mineral most commonly co-occurs with stibiopalladinite, native platinum, geversite, genkinite, chromite, chalcopyrite, pentlandite, and other rare platinum group minerals. ## Localities The most important and classic locality, from which type specimens originate, is the Driekop mine in the Bushveld Complex in South Africa. It has also been reported in other areas of this complex (Onverwacht, Mooihoek). Outside of South Africa, its occurrence has been confirmed in small quantities in the Fedorovo-Pansky intrusion on the Kola Peninsula in Russia and in the Stillwater Complex in Montana, USA.

Rarity

Very rare

For collectors

## Quality Criteria The quality of a stumpflite specimen is determined not by the mineral itself (which is microscopic), but by the richness and visibility of the mineral association in which it occurs. Samples from the Driekop mine are most valued, where stumpflite forms inclusions in polished sections, allowing for observation under a microscope. The presence of other rare platinum group minerals on the same specimen significantly increases its scientific and collector value. ## Popular Localities The only significant locality from a collector's perspective is the historical type locality – the Driekop mine in South Africa. Specimens from this location are classics and the standard for this mineral.

Care and storage

## Cleaning Stumpflite specimens, typically tiny inclusions in a rock matrix, are generally not cleaned. Any mechanical or chemical intervention could damage or destroy the delicate grains. If necessary, compressed air can be used to remove dust. ## What to Avoid Avoid contact with chemicals, acids, and ultrasonic cleaners. Do not subject the specimen to sudden temperature changes. Due to its nature (fine inclusions), avoid any abrasion or polishing of the surface. ## Storage Specimens containing stumpflite are best stored under stable conditions, in a closed display box, to protect them from dust and mechanical damage. They do not require special protection from light or humidity.