Sanmartinite is a very rare zinc tungstate mineral that typically appears as yellow to yellowish-brown tabular crystals. It is primarily identified by its distinct adamantine luster and its association with hydrothermal vein deposits, occurring most notably in Argentina.
Is this sanmartinite?
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 sanmartinite with a known reference. Sanmartinite sits at Mohs 4-4.5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: red brown.
- 3Read the lusterHold the specimen under a strong light. Luster: resinous.
- 4Match the color rangeCompare against the expected color range: brownish black, dark brown.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: tabular crystals.
Often confused with
Sanmartinite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Sanmartinite leaves red brown, Wolframite leaves reddish brown; luster reads resinous on Sanmartinite and submetallic on Wolframite.
How to tell apart: Streak differs, so Sanmartinite leaves red brown, Scheelite leaves white; luster reads resinous on Sanmartinite and vitreous to adamantine on Scheelite.
Often found alongside sanmartinite
Minerals reported to co-occur with sanmartinite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- ZnWO₄
- Mohs hardness
- 4-4.5
- Density
- 6.70 g/cm³
- Colors
- Streak
- Red brown
- Luster
- Resinous
- Transparency
- Translucent
- Crystal system
- Monoclinic
- Crystal habit
- Tabular crystals
- Cleavage
- On {010}, perfect
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A rare alteration product of scheelite in a quartz vein between granite and granite pegmatite intruding Precambrian crystalline schists
Where rockhounds find sanmartinite
Classic worldwide localities
- Los Cerrillos, seven km southwest of San Martín, San Luis Province, Argentina
Field-hunting tip
Where it forms: A rare alteration product of scheelite in a quartz vein between granite and granite pegmatite intruding Precambrian crystalline schists. If you start seeing willemite, scheelite, tourmaline in float, you are in the right ground. Typical habit: tabular crystals. Train your eye for that shape before scanning the outcrop.
Common questions
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Find sanmartinite on the map
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