Ferrorosemaryite is a rare phosphate mineral primarily found within complex granite pegmatite systems. It typically occurs as small, dark brown to black tabular crystals and is most notable for being a specific iron-dominant member of the fillowite group.
Is this ferrorosemaryite?
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 ferrorosemaryite with a known reference. Ferrorosemaryite sits at Mohs 4, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: greenish to brownish.
- 3Read the lusterHold the specimen under a strong light. Luster: resinous.
- 4Match the color rangeCompare against the expected color range: dark green, bronze.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: anhedral grains.
Often confused with
Ferrorosemaryite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Ferrorosemaryite leaves greenish to brownish, Fillowite leaves white; luster reads resinous on Ferrorosemaryite and subresinous to greasy on Fillowite.
How to tell apart: Triplite is the harder of the two (Mohs 5-5.5 vs. 4); streak differs, so Ferrorosemaryite leaves greenish to brownish, Triplite leaves white to brown; luster reads resinous on Ferrorosemaryite and vitreous to resinous on Triplite.
Often found alongside ferrorosemaryite
Minerals reported to co-occur with ferrorosemaryite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- □NaFe(FeAl)(PO₄)₃
- Mohs hardness
- 4
- Density
- 3.62 g/cm³
- Colors
- Streak
- Greenish to brownish
- Luster
- Resinous
- Transparency
- Transparent
- Crystal system
- Monoclinic
- Crystal habit
- Anhedral grains
- Cleavage
- Perfect on {010}; good on {1̄01}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- In cassiterite and columbite-tantalite-bearing granitic pegmatite
Where rockhounds find ferrorosemaryite
Classic worldwide localities
- Rubindi-Kabilizi pegmatite, 3 km WNW of Muhororo village, south of the Rubindi river, 50 km west of Kigali, Rwanda
Field-hunting tip
Where it forms: In cassiterite and columbite-tantalite-bearing granitic pegmatite. If you start seeing scorzalite, trolleite, montebrasite in float, you are in the right ground. Typical habit: anhedral grains. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify ferrorosemaryite?+
Where is ferrorosemaryite found?+
What rocks look like ferrorosemaryite?+
What minerals are found with ferrorosemaryite?+
What kind of rock does ferrorosemaryite form in?+
What is ferrorosemaryite used for?+
Find ferrorosemaryite on the map
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