Johnsomervilleite is a very rare phosphate mineral typically occurring as tiny, granular masses in phosphate-rich concretions. It is best known from the unique mineral localities of the Big Fish River area in Yukon, Canada, where it forms alongside other secondary phosphate minerals.
Is this johnsomervilleite?
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 johnsomervilleite with a known reference. Johnsomervilleite sits at Mohs 4.5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: pale brown; gray-brown with an olive tint.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous.
- 4Match the color rangeCompare against the expected color range: dark brown, blackish gray.
- 5Look at form & habitCrystal system: trigonal. Typical habit: colloform, dendritic, granular.
Often confused with
Johnsomervilleite vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside johnsomervilleite
Minerals reported to co-occur with johnsomervilleite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Na₃CaFe₁₁(PO₄)₉
- Mohs hardness
- 4.5
- Density
- 3.35 g/cm³
- Colors
- Dark brownBlackish gray
- Streak
- Pale brown; gray-brown with an olive tint
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Trigonal
- Crystal habit
- Colloform, dendritic, granular
- Cleavage
- Perfect, on {0001}, probable
- Rarity
- Rare
- Uses
- Collector
- Host rock
- As one of several primary accessory minerals forming clusters in podiform metamorphic segregations in kyanite-sillimanite-grade gneiss (Loch Quoich, Scotland)
Where rockhounds find johnsomervilleite
Classic worldwide localities
- Entrance to Glen Cosaidh, Loch Quoich, Inverness-shire, Scotland
- Sapucaia pegmatite mine, about 50 km east-southeast of Governador Valadares, Minas Gerais, Brazil
- Kiluli pegmatite, Rwanda
Field-hunting tip
Where it forms: As one of several primary accessory minerals forming clusters in podiform metamorphic segregations in kyanite-sillimanite-grade gneiss (Loch Quoich, Scotland). If you start seeing graftonite, apatite, jahnsite in float, you are in the right ground. Typical habit: colloform, dendritic, granular. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify johnsomervilleite?+
Where is johnsomervilleite found?+
What rocks look like johnsomervilleite?+
What minerals are found with johnsomervilleite?+
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What is johnsomervilleite used for?+
Find johnsomervilleite on the map
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