Johntomaite is a very rare phosphate mineral typically found in complex granite pegmatites. It most commonly occurs as small, dark brown tabular crystals often associated with other rare phosphate species in the Black Hills region of South Dakota.
Is this johntomaite?
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 johntomaite with a known reference. Johntomaite 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. Johntomaite leaves a dark grayish green streak.
- 3Read the lusterHold the specimen under a strong light. Johntomaite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: greenish black.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: tabular crystals.
Often confused with
Johntomaite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Johntomaite leaves dark grayish green, Bjarebyite leaves white; luster reads vitreous on Johntomaite and subadamantine on Bjarebyite.
How to tell apart: Trolleite is the harder of the two (Mohs 8.5 vs. 4-5); streak differs, so Johntomaite leaves dark grayish green, Trolleite leaves white.
How to tell apart: Streak differs, so Johntomaite leaves dark grayish green, Triphylite leaves white.
Often found alongside johntomaite
Minerals reported to co-occur with johntomaite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- BaFe²⁺₂Fe³⁺(PO₄)₂(OH,F)₂
- Mohs hardness
- 4-5
- Density
- 3.83 g/cm³
- Colors
- Streak
- Dark Grayish Green
- Luster
- Vitreous
- Transparency
- Opaque
- Crystal system
- Monoclinic
- Crystal habit
- Tabular Crystals
- Cleavage
- Perfect On {100}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Granite Pegmatites
Where rockhounds find johntomaite
Classic worldwide localities
- Spring Creek copper mine near Wilmington in the southern Flinders Ranges of South Australia
Field-hunting tip
Look in granite pegmatites country, the host setting where johntomaite typically forms. If you start seeing quartz, muscovite, triphylite in float, you are in the right ground. Field specimens usually show a tabular crystals habit, so train your eye for that shape before scanning the outcrop.
Common questions
How do you identify johntomaite?+
Where is johntomaite found?+
What rocks look like johntomaite?+
What minerals are found with johntomaite?+
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Find johntomaite on the map
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