Engelhauptite

Chemical formula: KCu²⁺₃(V⁵⁺₂O₇)(OH)₂Cl

Engelhauptite is a rare mineral from the vanadate group, forming characteristic blue-green, tabular crystals, discovered in the crater of the Tolbachik volcano.

## Characteristics Engelhauptite is a hydrated vanadate of potassium, copper, and chlorine. It forms thin, tabular crystals with a hexagonal outline, reaching up to 0.2 mm in size, which often arrange into rosette-like or spherical aggregates. It is a transparent mineral with a vitreous luster and a characteristic blue-green color. ## Physical Properties This mineral is relatively soft, with a Mohs hardness of approximately 3. It is brittle and exhibits perfect cleavage in one direction, parallel to the plane of the tablets. Its density, calculated based on the formula and cell parameters, is 3.63 g/cm³. ## Colors and Varieties Engelhauptite occurs in a uniform, blue-green color. No color or commercial varieties have been distinguished. ## History and Name The mineral's name honors Johann Paul Engelhaupt (born 1959), a German mineral collector from Bavaria, who specializes in Alpine minerals and has provided many valuable specimens for scientific research. Engelhauptite was approved as a new mineral by the International Mineralogical Association (IMA) in 2014 (IMA2014-064), and its description was published in 2015. The type locality is the Yadovitaya fumarole on the Second Northern Breakout of the Great Fissure Eruption of Tolbachik volcano in Kamchatka, Russia. ## Uses Due to its extreme rarity, small crystal sizes, and occurrence in a single, hard-to-reach location, engelhauptite has no industrial applications. It is solely an object of scientific and collecting interest for specialized micromineral collectors.

Properties

Mohs hardness: 3
Color: Yellow-brown to brown, typically with an olive green hue
Luster: Vitreous
Streak: Yellow
Density: 3.86
Cleavage: Perfect on {001}
Fracture: Irregular/Uneven
Transparency: Transparent,Translucent
Crystal system: Hexagonal

Diagnostic features

## Identification Engelhauptite can be identified by its characteristic blue-green color, tabular crystal habit with a hexagonal outline, and tendency to form rosette-like aggregates. The place of origin is also crucial – this mineral is known exclusively from the fumaroles of Tolbachik volcano. ## Distinguishing from Similar Minerals It can be confused with other secondary copper minerals from Tolbachik, such as lammerite or piipite. Definitive differentiation requires advanced analytical methods, such as Raman spectroscopy or X-ray diffraction (XRD), due to visual similarity and co-occurrence. ## Crystal Forms Crystals are thin, tabular, with a hexagonal outline. They usually occur as rosette-like or spherulitic aggregates, as well as single, scattered flakes on the surface of the host rock.

Geological environment

## Genesis Engelhauptite is a fumarolic mineral. It forms as a result of the reaction of volcanic gases rich in vanadium, chlorine, and potassium with atmospheric oxygen at high temperatures. It crystallizes directly from the gas phase (sublimate) on the surface of porous basaltic lava near volcanic exhalations. ## Mineral Associations This mineral co-occurs with other rare volcanic exhalation products from Tolbachik volcano, such as tenorite, hematite, lammerite, lykasite, piipite, popovite, as well as sulfates (aphthitalite, langbeinite) and sylvite. ## Localities The only confirmed locality of engelhauptite in the world is its type locality: Yadovitaya fumarole on Tolbachik volcano, Kamchatka, Far Eastern Federal District, Russia.

Rarity

Very rare

For collectors

## Quality Criteria The most valued specimens are those with well-formed, sharp crystals forming aesthetic, rosette-like aggregates. An intense, blue-green color and contrast with the light host rock are important. Due to the microscopic size of the crystals, specimens are evaluated under magnification. The abundance of crystals on the matrix significantly increases the specimen's value. ## Popular Localities All specimens available on the collector's market come from a single location – the fumarole of Tolbachik volcano in Kamchatka, Russia. This is the only known locality for this mineral.

Care and storage

## Cleaning Specimens should only be cleaned with compressed air to remove dust. Due to the fragility and small size of the crystals, contact with water, brushes, or other mechanical tools should be avoided. ## What to Avoid Contact with water, acids, and other chemicals that could damage or dissolve the mineral must be absolutely avoided. The crystals are very brittle and susceptible to mechanical damage. They should be protected from high temperatures and sudden temperature changes. ## Storage It is recommended to store specimens in specialized, sealed "micromount" boxes, which protect against dust, moisture, and mechanical damage. Avoid exposure to direct sunlight and store in stable humidity conditions.

External references

https://www.mindat.org/min-43875.html