Stronadelphite is a rare strontium-dominant member of the apatite group that typically forms as small, hexagonal prismatic crystals. It is primarily found in complex alkaline igneous environments and is highly valued by advanced collectors due to its rarity compared to common fluorapatite.
Is this stronadelphite?
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 stronadelphite with a known reference. Stronadelphite sits at Mohs 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: vitreous.
- 4Match the color rangeCompare against the expected color range: colorless, white, gray.
- 5Look at form & habitCrystal system: hexagonal. Typical habit: prismatic crystals.
Often confused with
Stronadelphite vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside stronadelphite
Minerals reported to co-occur with stronadelphite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Sr₅(PO₄)₃F
- Mohs hardness
- 5
- Density
- 3.915 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Hexagonal
- Crystal habit
- Prismatic crystals
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- From hydrothermal alteration of peralkaline pegmatite is a sinuous and branched vein cross-cutting inequigranular nepheline syenite in an alkaline massif
Where rockhounds find stronadelphite
Classic worldwide localities
- Belovitovoye peralkaline pegmatite, Kirovskii apatite mine, Mt. Kukisvumchorr, Khibiny alkaline complex, Kola peninsula, Russia (type locality)
- Mt. Alluaiv, Lovozero complex, Kola peninsula, Russia, as rims on fluorapatite
Field-hunting tip
Where it forms: From hydrothermal alteration of peralkaline pegmatite is a sinuous and branched vein cross-cutting inequigranular nepheline syenite in an alkaline massif. If you start seeing natrolite, microcline, aegirine in float, you are in the right ground. Typical habit: prismatic crystals. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify stronadelphite?+
Where is stronadelphite found?+
What rocks look like stronadelphite?+
What minerals are found with stronadelphite?+
What kind of rock does stronadelphite form in?+
What is stronadelphite used for?+
Find stronadelphite on the map
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