Rudenkoite is a rare strontium aluminum hydroxide, typically white. Associated minerals include prehnite, calcite and spinel. It was first described from Emelʼdzhaksky phlogopite deposit, Aldan province, Aldan Shield, southern Yakutsk, Russia.
Is this rudenkoite?
4-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 rudenkoite with a known reference. Rudenkoite sits at Mohs 1.5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: white.
- 3Match the color rangeCompare against the expected color range: white.
- 4Look at form & habitCrystal system: monoclinic. Typical habit: aggregates, pseudomorphous, radial.
Often confused with
Rudenkoite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Laurionite is the harder of the two (Mohs 3-3.5 vs. 1.5).
How to tell apart: Penfieldite is the harder of the two (Mohs 3-4 vs. 1.5).
How to tell apart: Paralaurionite is the harder of the two (Mohs 3 vs. 1.5).
Often found alongside rudenkoite
Minerals reported to co-occur with rudenkoite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Sr₃Al₃.₅Si₃.₅O₁₀(OH,O)₈Cl₂·H₂O
- Mohs hardness
- 1.5
- Density
- 3.17 g/cm³
- Colors
- Streak
- White
- Transparency
- Translucent
- Crystal system
- Monoclinic
- Crystal habit
- Aggregates, pseudomorphous, radial
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Formed in the last stages of (metasomatic) prehnitization, in garnet-wollastonite metamorphic rock (skarn) at the contact between pegmatite and calcite marble
Where rockhounds find rudenkoite
Classic worldwide localities
- Emelʼdzhaksky phlogopite deposit, Aldan province, Aldan Shield, southern Yakutsk, Russia
Field-hunting tip
Where it forms: Formed in the last stages of (metasomatic) prehnitization, in garnet-wollastonite metamorphic rock (skarn) at the contact between pegmatite and calcite marble. If you start seeing prehnite, calcite, spinel in float, you are in the right ground. Typical habit: aggregates, pseudomorphous, radial. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify rudenkoite?+
Where is rudenkoite found?+
What rocks look like rudenkoite?+
What minerals are found with rudenkoite?+
What kind of rock does rudenkoite form in?+
What is rudenkoite used for?+
Find rudenkoite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
