Millsite is a rare secondary tellurite mineral typically found as delicate, pale yellow crusts or crystalline aggregates in oxidized ore deposits. It is primarily known from the Tombstone District of Arizona, where it forms in association with other rare tellurium species. Due to its extreme rarity and small crystal size, it is almost exclusively sought after by advanced micromount mineral collectors.
Is this millsite?
5-step field checkRun through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.
- 1Test the hardnessTry to scratch millsite with a known reference. Millsite sits at Mohs 2 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Millsite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Millsite typically shows a pearly luster.
- 4Match the color rangeCompare against the expected color range: yellow, pale yellow.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: crusts, aggregates.
Often confused with
Millsite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Streak differs — Millsite leaves white, Teineite leaves pale blue; luster reads pearly on Millsite and vitreous on Teineite.
How to tell apart: Emmonsite is the harder of the two (Mohs 5 vs. 2); streak differs — Millsite leaves white, Emmonsite leaves pale yellow; luster reads pearly on Millsite and vitreous on Emmonsite.
Often found alongside millsite
Minerals reported to co-occur with millsite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- K₂TeO₃·3H₂O
- Mohs hardness
- 2
- Density
- 3.37 g/cm³
- Colors
- Streak
- White
- Luster
- Pearly
- Transparency
- Translucent
- Crystal system
- Orthorhombic
- Crystal habit
- Crusts, Aggregates
- Cleavage
- Perfect
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Oxidized Tellurium-bearing Ore Deposits
- Typical price
- $50-300 for small micro-mounts
Where rockhounds find millsite
Classic worldwide localities
- Tombstone District, Arizona, USA
Field-hunting tip
Look in oxidized tellurium-bearing ore deposits country — that is the host setting where millsite typically forms. If you start seeing tellurite, paratellurite, quetzalcoatlite in float, you are in the right ground. Field specimens usually show a crusts, aggregates habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find millsite on the map
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