Tassieite is a very rare hydrated calcium iron phosphate mineral typically found as small, thin platy crystals or crusts. It is most famous for its occurrence in the tin-bearing deposits of Tasmania, often associated with vivianite in weathered zones.
Is this tassieite?
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 tassieite with a known reference. Tassieite sits at Mohs 2, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: light green.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous.
- 4Match the color rangeCompare against the expected color range: dark green.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: inclusions.
Often confused with
Tassieite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Tassieite leaves light green, Vivianite leaves white, altering to dark blue, brown.
How to tell apart: Gorceixite is the harder of the two (Mohs 6 vs. 2); streak differs, so Tassieite leaves light green, Gorceixite leaves white.
Often found alongside tassieite
Minerals reported to co-occur with tassieite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- NaCa₂Mg₃Fe₂Fe(PO₄)₆·2H₂O
- Mohs hardness
- 2
- Density
- 3.45 g/cm³
- Colors
- Streak
- Light green
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Orthorhombic
- Crystal habit
- Inclusions
- Cleavage
- Perfect to good on {100} and on a second direction at 60o to the first
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A late-stage, low-temperature mineral formed by hydrothermal alteration of stornesite-(Y), wagnerite and fluorapatite in the core of a fluorapatite nodule in regionally metamorphosed and fractured gneissic rocks
Where rockhounds find tassieite
Classic worldwide localities
- Johnston Fjord, Stornes Peninsula, Larsemann Hills, Prydz Bay, East Antarctica (type locality)
Field-hunting tip
Where it forms: A late-stage, low-temperature mineral formed by hydrothermal alteration of stornesite-(Y), wagnerite and fluorapatite in the core of a fluorapatite nodule in regionally metamorphosed and fractured gneissic rocks. If you start seeing stornesite-, wagnerite, fluorapatite in float, you are in the right ground. Typical habit: inclusions. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify tassieite?+
Where is tassieite found?+
What rocks look like tassieite?+
What minerals are found with tassieite?+
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Find tassieite on the map
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