Morrisonite

Chemical formula: Ca₁₁(As₃+V₄+₂V₅+₁₀As₅+₆O₅₁)₂·₇₈H₂O

Morrisonite is an extremely rare, hydrated calcium arsenate-vanadate, forming microscopic, acicular crystals of an intensely orange color.

## Characteristics Morrisonite is a mineral from the arsenate and vanadate group, distinguished by its exceptionally complex chemical composition. It occurs as microscopic, acicular or bladed crystals, which form radiating aggregates, rosettes, or crusts. Individual crystals rarely exceed 1 mm in length. Due to their small size, visual features are mainly discernible under magnification. ## Physical Properties Morrisonite crystals are flexible and exhibit a luster described as silky or vitreous. Hardness and density have not been precisely measured due to the small size and rarity of the material. The mineral is translucent. ## Colors and Varieties Morrisonite is characterized by a vivid, orange color. No varieties are known. ## History and Name The mineral was officially recognized by the International Mineralogical Association (IMA) in 2016. Its name honors Philip Morrison (b. 1945), an American mineral collector from Arizona, who specializes in vanadium minerals and is a co-discoverer of several new mineral species. Morrisonite was discovered at the West-Sunday uranium and vanadium mine in San Miguel County, Colorado, USA. ## Applications Morrisonite has no industrial applications. Its significance is purely scientific and collectible, as a unique and newly discovered mineral.

Properties

Luster: Silky
Streak: Orange
Transparency: Translucent
Crystal system: Monoclinic

Diagnostic features

## Identification Morrisonite is identified by its unique appearance – orange, acicular crystals forming radiating aggregates. Key to identification is the locality (West-Sunday mine) and co-occurrence with other rare vanadates. Final confirmation requires advanced analytical methods, such as Raman spectroscopy or chemical analysis (EDS). ## Distinguishing from Similar Minerals It can be confused with other orange, acicular secondary minerals from the vanadate group, such as pascoite or hewettite. Morrisonite differs from them by subtle variations in hue, aggregate form, and most importantly, its chemical composition, which contains both vanadium and arsenic. ## Crystal Forms The mineral forms very fine, elongated crystals with an acicular or bladed habit. These crystals combine into characteristic, radiating or stellate aggregates and rosettes, and also form thin crusts on the host rock.

Geological environment

## Genesis Morrisonite is a secondary mineral that forms in the oxidation zone of uranium-vanadium deposits hosted in sandstones. It forms as a result of the weathering of primary ore minerals under low temperature and pressure conditions, in the presence of waters rich in dissolved oxygen, calcium, vanadium, and arsenic. ## Mineral Associations This mineral occurs in association with other rare vanadium and uranium minerals. It most commonly co-occurs with gypsum, hewettite, pascoite, martyite, and also rare vanadium arsenates such as schindlerite and fianelite. These minerals form colorful crusts on sandstone. ## Localities The only confirmed locality for morrisonite in the world is its type locality – the West-Sunday mine, located in the Slick Rock district, San Miguel County, Colorado, USA.

Rarity

Extremely rare

For collectors

## Quality Criteria The quality of morrisonite specimens is assessed based on the richness and aesthetics of the crystal aggregates. Most prized are specimens with well-formed, radiating rosettes of an intensely orange color, clearly contrasting with the light background of the host rock (sandstone). The absence of damage to the delicate crystals and the presence of associated minerals, which enhance the scientific and visual value of the specimen, are also important. ## Popular Localities The only source of morrisonite specimens is the West-Sunday mine in Colorado, USA. Material from this locality is extremely rare and sought after by specialized systematic mineral collectors and those focusing on rare species.

Care and storage

## Cleaning Morrisonite specimens are extremely delicate and susceptible to mechanical damage. Cleaning is not recommended. Any attempts to remove dust should be limited to very careful use of a soft brush or a photographic air blower, without touching the crystals. ## What to Avoid Contact with water, chemicals, ultrasound, and sudden temperature changes must be strictly avoided. The crystals are brittle and fragile. As a hydrated mineral, it may be sensitive to changes in humidity and elevated temperatures, which can lead to its dehydration and destruction. ## Storage Specimens should be stored in stable conditions, in closed, padded "micromount" boxes, to protect them from dust, shocks, and humidity changes. They should not be exposed to direct sunlight.

Sources

IMA Mineral List (CNMNC)