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, 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.