Rynersonite is an extremely rare tantalum mineral that typically occurs as small, resinous tabular crystals. It is primarily found within complex granite pegmatites and is often associated with other rare earth minerals.
Is this rynersonite?
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 rynersonite with a known reference. Rynersonite sits at Mohs ~4.5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: white.
- 3Read the lusterHold the specimen under a strong light. Luster: dull, earthy in aggregates.
- 4Match the color rangeCompare against the expected color range: beige white, pink.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: tabular crystals.
Often confused with
Rynersonite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Euxenite-(Y) is the harder of the two (Mohs 5.5-6.5 vs. ~4.5); streak differs, so Rynersonite leaves white, Euxenite-(Y) leaves yellowish, grayish, or reddish brown; luster reads dull, earthy in aggregates on Rynersonite and brilliant submetallic, waxy to resinous on fractures on Euxenite-(Y).
How to tell apart: Streak differs, so Rynersonite leaves white, Samarskite-(Y) leaves dark reddish brown to black, yellow-brown; gray when altered; luster reads dull, earthy in aggregates on Rynersonite and vitreous to resinous, may be submetallic, splendent; externally dull on Samarskite-(Y).
Often found alongside rynersonite
Minerals reported to co-occur with rynersonite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- CaTa₂O₆
- Mohs hardness
- ~4.5
- Density
- 6.402 g/cm³
- Colors
- Beige whitePink
- Streak
- White
- Luster
- Dull, earthy in aggregates
- Transparency
- Transparent
- Crystal system
- Orthorhombic
- Crystal habit
- Tabular crystals
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A rare alteration product of earlier Nb–Ta minerals in some granite pegmatites
Where rockhounds find rynersonite
Classic worldwide localities
- Himalaya and San Diego mines, Mesa Grande district, San Diego Co., California, USA
- Brown Derby No. 1 pegmatite, Quartz Creek district, Gunnison Co., Colorado, USA
- Wampewo pegmatite, Gamba Hill, near Kampala, southwest Uganda
Field-hunting tip
Where it forms: A rare alteration product of earlier Nb–Ta minerals in some granite pegmatites. If you start seeing fersmite, stibiotantalite, cassiterite 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 rynersonite on the map
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