Howardevansite
Chemical formula: NaCu<sup>2+</sup>Fe<sup>3+</sup><sub>2</sub>(V<sup>5+</sup>O<sub>4</sub>)<sub>3</sub>
Howardevansite is a very rare sodium, copper, and iron vanadate, forming black, tabular crystals in volcanic exhalations.
Properties
- Mohs hardness
- 3
- Luster
- Submetallic
- Streak
- Reddish-brown
- Density
- 3.89
- Cleavage
- Good on {010} and {001}
- Fracture
- Uneven
- Transparency
- Opaque
- Crystal system
- Triclinic
Diagnostic features
## Identification Characteristic features of howardevansite include its black color, reddish-brown streak, and submetallic luster. However, crucial for identification is its specific environment of occurrence – as a sublimation product in volcanic fumaroles. It occurs as very small, tabular crystals. ## Distinguishing from Similar Minerals It can be confused with other black, opaque minerals found in the same environment, such as tenorite or hematite. However, tenorite has a black streak, and hematite, although it may have a similar one, differs in crystal habit and often co-occurring minerals. Definitive identification is almost exclusively possible using advanced analytical methods, such as X-ray diffraction (XRD) or chemical microanalysis (EDS). ## Crystal Forms Crystals are most often tabular, flattened parallel to {010}, or short-prismatic. They usually form aggregates of subparallel crystals, rosette aggregates, or druses covering the rock surface.
Geological environment
## Genesis Howardevansite is a secondary mineral, forming under very specific conditions. It crystallizes directly from volcanic gases (sublimate) in high-temperature fumaroles. ## Mineral Associations At the type locality (Izalco volcano), it co-occurs with minerals such as shcherbinaite, stoiberite, fingerite, ziesite, bannermanite, thenardite, and euchlorine. At Tolbachik volcano, its associated minerals include langbeinite, hematite, tenorite, and aphthitalite. ## Localities This is a mineral with very limited occurrence. The most important and confirmed localities are: - Izalco volcano in Sonsonate Department, El Salvador (type locality). - Arsenatnaya fumarole on the second slag cone of the northern breach of the Great Fissure Eruption of Tolbachik volcano in Kamchatka, Russia.
Rarity
Very rare
For collectors
## Quality Criteria The quality of collectible howardevansite specimens, being a typical micromineral, is assessed based on several criteria. Samples with well-formed, sharp, and undamaged crystals are most highly valued. The abundance of the mineral on the rock matrix and visually attractive associations with other rare fumarolic minerals are also important. ## Popular Localities Specimens available on the collector's market come almost exclusively from Tolbachik volcano in Kamchatka. Material from the type locality in El Salvador is practically unavailable and primarily of historical value.
Care and storage
## Cleaning Howardevansite specimens should only be dry-cleaned, using a soft brush or compressed air to remove dust. Contact with water, and especially with chemical solutions, can lead to damage or destruction of the mineral. ## What to Avoid It is absolutely essential to avoid washing in water, cleaning in ultrasonic cleaners, and contact with acids and other chemicals. The mineral is soft and brittle, therefore requiring careful handling to avoid mechanical damage. ## Storage It is recommended to store specimens in stable conditions, away from moisture and contaminants. The best solution is to place them in tightly sealed "micromount" boxes, which protect against dust and physical damage.