Tewite
Chemical formula: (K<sub>1.5</sub>☐<sub>0.5</sub>)(Te<sup>4+</sup><sub>1.25</sub>W<sup>6+</sup><sub>0.25</sub>☐<sub>0.5</sub>)<sub>2</sub>W<sup>6+</sup><sub>5</sub>O<sub>19</sub>
Tewite is an extremely rare potassium tellurite and tungstate, forming small, tabular, yellow crystals.
Properties
- Luster
- Adamantine to greasy
- Streak
- Light yellow
- Density
- 6.18
- Cleavage
- Perfect on {001}
- Transparency
- Translucent
- Crystal system
- Tetragonal
Diagnostic features
## Identification Amateur identification of tewite is practically impossible. Indicative features may include: yellow color, platy or micaceous crystal habit, high density, and co-occurrence with other rare tellurium and tungsten minerals. Definitive identification requires advanced analytical techniques such as X-ray diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDS). ## Distinguishing from Similar Minerals Tewite can be confused with other secondary yellow minerals, such as tungstite or ferritungstite. However, tungstite more often has an earthy habit or forms coatings, less frequently distinct crystals. It shows the greatest similarity to other rare tellurites and tellurates, from which differentiation is almost exclusively possible by laboratory methods. Its characteristic, thin-tabular habit is an important diagnostic clue. ## Crystal Forms Tewite crystals are very small, thin, and tabular (platy), with a square or octagonal outline. They usually occur as loose, mica-like aggregates (micaceous aggregates) or as thin coatings on the host rock.
Geological environment
## Genesis Tewite is a secondary mineral, forming in the oxidation zones of low-temperature, epithermal quartz veins. It forms as a result of weathering and alteration of primary minerals containing tellurium and tungsten under strongly oxidizing conditions. ## Mineral Associations This mineral occurs in association with other rare tellurium minerals, such as ottoite, paratellurite, and tellurite. It also co-occurs with tungsten minerals, mainly tungstite and scheelite. Associated minerals also include quartz, calcite, and iron oxides and hydroxides (e.g., goethite). ## Localities The only confirmed and described locality of tewite in the world is its type locality – the Bird Nest Drift area on Otto Mountain, near Baker, San Bernardino County, California, USA.
Rarity
Extremely rare
For collectors
## Quality Criteria The quality of tewite specimens, being a micromineral, is assessed based on different criteria than for minerals forming large crystals. Highly valued are rich aggregates of well-formed, though still microscopic, platy crystals. Additional value is provided by the presence of tewite in association with other rare and well-defined associated minerals, especially ottoite. A contrasting quartz matrix also enhances the visual appeal of the specimen. ## Popular Localities All known and available tewite specimens in collections come from a single location in the world – its type locality on Otto Mountain in California. This is the only locality from which this mineral has been obtained.
Care and storage
## Cleaning Tewite specimens are extremely delicate and rare. Mechanical cleaning is highly risky and not recommended. Any attempts to use brushes, needles, or ultrasonic cleaners can irrevocably destroy the fragile lamellae of the mineral. If necessary, dust can be removed very carefully using a stream of compressed air from a safe distance. ## What to Avoid Avoid contact with any liquids, including water and chemicals, as their effect on the mineral is unknown. Absolutely protect from impacts, vibrations, and abrasions, which can cause aggregates to disintegrate due to perfect cleavage. Store away from sources of dust. ## Storage The safest storage method is to place the specimen in a closed, padded "micromount" box, which protects against mechanical damage and dust. The label should be on the box, not on the specimen itself.