Tetraferriphlogopite is a rare member of the mica group characterized by the substitution of Fe³⁺ for silicon in the tetrahedral site of the crystal lattice. Collectors typically look for its distinct dark brown to reddish-brown platy, pseudo-hexagonal crystals embedded in carbonatite or alkaline silicate rocks.
Is this tetraferriphlogopite?
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 tetraferriphlogopite with a known reference. Tetraferriphlogopite sits at Mohs 2.5-3, 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: pearly.
- 4Match the color rangeCompare against the expected color range: brown, dark brown, yellowish-brown, reddish-brown.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: platy crystals, pseudo-hexagonal flakes.
Often confused with
Tetraferriphlogopite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Luster reads pearly on Tetraferriphlogopite and splendent to submetallic, vitreous, pearly on cleavage on Biotite.
How to tell apart: Tetraferriphlogopite is noticeably harder (Mohs 2.5-3 vs. ~1.5); streak differs, so Tetraferriphlogopite leaves white, Vermiculite leaves greenish white; luster reads pearly on Tetraferriphlogopite and dull to pearly, bronzy on Vermiculite.
Often found alongside tetraferriphlogopite
Minerals reported to co-occur with tetraferriphlogopite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- KMg₃(Fe³⁺Si₃O₁₀)(OH)₂
- Mohs hardness
- 2.5-3
- Density
- 2.7-2.9 g/cm³
- Streak
- White
- Luster
- Pearly
- Transparency
- Translucent
- Crystal system
- Monoclinic
- Crystal habit
- Platy crystals, pseudo-hexagonal flakes
- Cleavage
- Perfect basal
- Rarity
- Uncommon
- Uses
- Collector
- Host rock
- alkaline igneous rocks, carbonatites
Where rockhounds find tetraferriphlogopite
Classic worldwide localities
- Kovdor Massif, Russia
- Magnet Cove, USA
- Jacupiranga, Brazil
- Tapira, Brazil
Field-hunting tip
Where it forms: alkaline igneous rocks, carbonatites. If you start seeing magnetite, apatite, calcite in float, you are in the right ground. Typical habit: platy crystals, pseudo-hexagonal flakes. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify tetraferriphlogopite?+
Where is tetraferriphlogopite found?+
What rocks look like tetraferriphlogopite?+
What minerals are found with tetraferriphlogopite?+
What kind of rock does tetraferriphlogopite form in?+
What is tetraferriphlogopite used for?+
Find tetraferriphlogopite on the map
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