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.

Hardness

2.5-3

Mohs

Luster

Pearly

Streak

White

Transparency

Translucent

mineraluncommonMica Group family

Tetraferriphlogopite

Hardness: 2.5-3
Luster: Pearly
Streak: White
Transparency: Translucent

No image

Is this tetraferriphlogopite?

5-step field check

Run through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.

1
Test the hardness
Try 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.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Tetraferriphlogopite leaves a white streak.
3
Read the luster
Hold the specimen under a strong light. Tetraferriphlogopite typically shows a pearly luster.
4
Match the color range
Compare against the expected color range: brown, dark brown, yellowish-brown, reddish-brown.
5
Look at form & habit
Crystal 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.

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
Colors: Brown Dark Brown Yellowish-brown Reddish-brown
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
Typical price: $10-50 per specimen

Where rockhounds find tetraferriphlogopite

Classic worldwide localities

Kovdor Massif, Russia
Magnet Cove, USA
Jacupiranga, Brazil
Tapira, Brazil

Field-hunting tip

Look in alkaline igneous rocks, carbonatites country — that is the host setting where tetraferriphlogopite typically forms. If you start seeing magnetite, apatite, calcite in float, you are in the right ground. Field specimens usually show a platy crystals, pseudo-hexagonal flakes habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify tetraferriphlogopite?+

Mohs hardness is 2.5-3. It typically shows a pearly luster. The streak is white. Common colors include brown, dark brown, yellowish-brown, reddish-brown.

Where is tetraferriphlogopite found?+

Notable localities include Kovdor Massif, Russia; Magnet Cove, USA; Jacupiranga, Brazil; Tapira, Brazil.

How much is tetraferriphlogopite worth?+

Typical asking prices fall in the range of $10-50 per specimen. Quality, size, and provenance can move individual specimens well outside that range.

What rocks look like tetraferriphlogopite?+

Tetraferriphlogopite is most often confused with Phlogopite, Biotite, Vermiculite. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with tetraferriphlogopite?+

Tetraferriphlogopite commonly co-occurs with Magnetite, Apatite, Calcite, Diopside. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does tetraferriphlogopite form in?+

Tetraferriphlogopite typically forms in alkaline igneous rocks, carbonatites. Working float back to the host body is the standard way to chase a fresh occurrence.

What is tetraferriphlogopite used for?+

Tetraferriphlogopite is used in collector.

Find tetraferriphlogopite on the map

RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.