Sejkoraite-(Y) is a rare yttrium uranium sulfate that forms yellow-orange to orange crystalline aggregates. Associated minerals include pseudojohannite, rabejacite and uranopilite. It was first described from the Červená vein, Jáchymov (St. Joachimsthal) ore district, Western Bohemia, Czech Republic.
Is this sejkoraite-(y)?
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 sejkoraite-(y) with a known reference. Sejkoraite-(Y) 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. Streak: pale yellow-to-yellow.
- 3Read the lusterHold the specimen under a strong light. Luster: strong vitreous.
- 4Match the color rangeCompare against the expected color range: yellow-orange, orange.
- 5Look at form & habitCrystal system: triclinic. Typical habit: crystalline aggregates.
Often confused with
Sejkoraite-(Y) vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Mixite is the harder of the two (Mohs 3-4 vs. ~2); luster reads strong vitreous on Sejkoraite-(Y) and vitreous, silky in aggregates on Mixite.
How to tell apart: Agardite-(Y) is the harder of the two (Mohs 3-4 vs. ~2); streak differs, so Sejkoraite-(Y) leaves pale yellow-to-yellow, Agardite-(Y) leaves greenish white; luster reads strong vitreous on Sejkoraite-(Y) and vitreous on Agardite-(Y).
How to tell apart: Streak differs, so Sejkoraite-(Y) leaves pale yellow-to-yellow, Zálesíite leaves white; luster reads strong vitreous on Sejkoraite-(Y) and vitreous to resinous on Zálesíite.
Often found alongside sejkoraite-(y)
Minerals reported to co-occur with sejkoraite-(y). Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Y₂[(UO₂)₈O₆(SO₄)₄(OH)₂]·26H₂O
- Mohs hardness
- ~2
- Density
- 4.04 g/cm³
- Colors
- Streak
- Pale yellow-to-yellow
- Luster
- Strong vitreous
- Transparency
- Transparent to translucent
- Crystal system
- Triclinic
- Crystal habit
- Crystalline aggregates
- Cleavage
- Perfect on {100}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Coating surfaces of relic primary minerals: uraninite, chalcopyrite, and tennantite, altered in an acidic oxidizing environment
Where rockhounds find sejkoraite-(y)
Classic worldwide localities
- Jáchymov (Czech Republic)
Field-hunting tip
Where it forms: Coating surfaces of relic primary minerals: uraninite, chalcopyrite, and tennantite, altered in an acidic oxidizing environment. If you start seeing pseudojohannite, rabejacite, uranopilite in float, you are in the right ground. Typical habit: crystalline aggregates. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify sejkoraite-(y)?+
Where is sejkoraite-(y) found?+
Is sejkoraite-(y) safe to handle?+
What rocks look like sejkoraite-(y)?+
What minerals are found with sejkoraite-(y)?+
What kind of rock does sejkoraite-(y) form in?+
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Find sejkoraite-(y) on the map
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