Kobeite-(Y) is a rare radioactive complex oxide mineral primarily found in granitic pegmatites. It typically occurs as small, dark prismatic crystals that often exhibit a brownish-black color and vitreous luster.
Is this kobeite-(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 kobeite-(y) with a known reference. Kobeite-(Y) sits at Mohs 5.5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: reddish brown.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous to resinous.
- 4Match the color rangeCompare against the expected color range: black, brown, brownish black, dark brown.
- 5Look at form & habitCrystal system: cubic. Typical habit: metamict, prismatic, radial.
Often confused with
Kobeite-(Y) vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Kobeite-(Y) leaves reddish brown, Euxenite-(Y) leaves yellowish, grayish, or reddish brown; luster reads vitreous to resinous on Kobeite-(Y) and brilliant submetallic, waxy to resinous on fractures on Euxenite-(Y).
How to tell apart: Streak differs, so Kobeite-(Y) leaves reddish brown, Samarskite-(Y) leaves dark reddish brown to black, yellow-brown; gray when altered.
How to tell apart: Streak differs, so Kobeite-(Y) leaves reddish brown, Fergusonite-(Y) leaves brown, yellow-brown, greenish gray; luster reads vitreous to resinous on Kobeite-(Y) and dull; vitreous to submetallic on fractures on Fergusonite-(Y).
Often found alongside kobeite-(y)
Minerals reported to co-occur with kobeite-(y). Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- (Y,U,U)(Ti,Nb)₂(O,OH)₆
- Mohs hardness
- 5.5
- Density
- 4.60 g/cm³
- Streak
- Reddish brown
- Luster
- Vitreous to resinous
- Transparency
- Transparent to translucent
- Crystal system
- Cubic
- Crystal habit
- Metamict, prismatic, radial
- Cleavage
- Perpendicular to the length, probably a parting
- Rarity
- Rare
- Uses
- Collector
- Host rock
- In granite pegmatites (Japan); in a stream cobble of graphic granite (Paringa River, New Zealand)
Where rockhounds find kobeite-(y)
Classic worldwide localities
- Shiraishi pegmatite, Oyama, and in the Ushio mine, Omiya, Kyoto Prefecture, Japan
- Senogawa-machi, Hiroshima Prefecture, Japan
- A cobble found in the Paringa River, about 1.2 km upstream from the Weheka-Paringa highway bridge, South Westland, New Zealand
Field-hunting tip
Where it forms: In granite pegmatites (Japan); in a stream cobble of graphic granite (Paringa River, New Zealand). If you start seeing anatase, parisite, zircon in float, you are in the right ground. Typical habit: metamict, prismatic, radial. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify kobeite-(y)?+
Where is kobeite-(y) found?+
Is kobeite-(y) safe to handle?+
What rocks look like kobeite-(y)?+
What minerals are found with kobeite-(y)?+
What kind of rock does kobeite-(y) form in?+
What is kobeite-(y) used for?+
Find kobeite-(y) on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
