Decrespignyite-(Y) is a rare secondary mineral found primarily as tiny, vibrant blue to emerald-green platy crystals or crusts. It is most famous from the Mount Painter region in Australia, where it occurs within vugs of iron-rich host rocks. Its unique composition, involving both copper and yttrium, makes it a highly sought-after prize for advanced mineral collectors.
Is this decrespignyite-(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 decrespignyite-(y) with a known reference. Decrespignyite-(Y) sits at Mohs ~4, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: pale blue.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous to pearly.
- 4Match the color rangeCompare against the expected color range: intense royal blue, turquoise blue.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: efflorescences, globular.
Often confused with
Decrespignyite-(Y) vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Luster reads vitreous to pearly on Decrespignyite-(Y) and adamantine to vitreous; silky if fibrous; dull to earthy if massive on Malachite.
How to tell apart: Decrespignyite-(Y) is noticeably harder (Mohs ~4 vs. 1-2); streak differs, so Decrespignyite-(Y) leaves pale blue, Aurichalcite leaves light blue; luster reads vitreous to pearly on Decrespignyite-(Y) and silky to pearly on Aurichalcite.
Often found alongside decrespignyite-(y)
Minerals reported to co-occur with decrespignyite-(y). Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Y₄Cu(CO₃)₄Cl(OH)₅·2H₂O
- Mohs hardness
- ~4
- Density
- 3.64 g/cm³
- Colors
- Intense royal blueTurquoise blue
- Streak
- Pale blue
- Luster
- Vitreous to pearly
- Transparency
- Transparent
- Crystal system
- Monoclinic
- Crystal habit
- Efflorescences, globular
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A rare secondary mineral in the oxidized zone of a copper deposit, the source of rare-earths enigmatic, perhaps from surrounding sediments
Where rockhounds find decrespignyite-(y)
Classic worldwide localities
- Paratoo copper mine, 30 km southwest of Yunta, Olary district, South Australia
Field-hunting tip
Where it forms: A rare secondary mineral in the oxidized zone of a copper deposit, the source of rare-earths enigmatic, perhaps from surrounding sediments. If you start seeing caysichite-, donnayite-, kamphaugite- in float, you are in the right ground. Typical habit: efflorescences, globular. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify decrespignyite-(y)?+
Where is decrespignyite-(y) found?+
Is decrespignyite-(y) safe to handle?+
What rocks look like decrespignyite-(y)?+
What minerals are found with decrespignyite-(y)?+
What kind of rock does decrespignyite-(y) form in?+
What is decrespignyite-(y) used for?+
Find decrespignyite-(y) on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
