Eggletonite is a rare manganese silicate mineral that typically appears as brown to reddish-brown tabular crystals or massive grains. It is structurally related to the pyrosmalite group and is most famous for its occurrences in specific alkaline igneous environments. Collectors prize it primarily for its distinct crystal habits and association with rare-earth mineral assemblages.

Hardness

3-4

Mohs

Luster

Vitreous

Streak

White

Transparency

Translucent

mineralrarePyrosmalite Group family

Eggletonite

Hardness: 3-4
Luster: Vitreous
Streak: White
Transparency: Translucent

Is this eggletonite?

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 eggletonite with a known reference. Eggletonite sits at Mohs 3-4 — softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Eggletonite leaves a white streak.
3
Read the luster
Hold the specimen under a strong light. Eggletonite typically shows a vitreous luster.
4
Match the color range
Compare against the expected color range: brown, reddish-brown.
5
Look at form & habit
Crystal system: trigonal. Typical habit: tabular crystals, massive, granular.

Often confused with

Eggletonite vs. its common look-alikes — and how to tell them apart in the field.

Often found alongside eggletonite

Minerals reported to co-occur with eggletonite. Spotting these in float or country rock is a strong cue you are in the right ground.

All properties

Chemical formula: (Na,Ca,K)₈(Mn,Fe,Mg,Zn)₈(Si,Al)₁₂O₃₀(OH,F)₁₀·4H₂O
Mohs hardness: 3-4
Density: 3.0-3.1 g/cm³
Colors: Brown Reddish-brown
Streak: White
Luster: Vitreous
Transparency: Translucent
Crystal system: Trigonal
Crystal habit: Tabular Crystals, Massive, Granular
Cleavage: Perfect Basal
Rarity: Rare
Uses: Collector
Host rock: Nepheline Syenite Pegmatites, Hydrothermal Veins
Typical price: $50-300 per specimen depending on size and quality

Where rockhounds find eggletonite

Classic worldwide localities

Big Rock Quarry, Arkansas, USA
Franklin, New Jersey, USA
Khibiny Massif, Russia

Field-hunting tip

Look in nepheline syenite pegmatites, hydrothermal veins country — that is the host setting where eggletonite typically forms. If you start seeing aegirine, microcline, pectolite in float, you are in the right ground. Field specimens usually show a tabular crystals, massive, granular habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify eggletonite?+

Mohs hardness is 3-4. It typically shows a vitreous luster. The streak is white. Common colors include brown, reddish-brown.

Where is eggletonite found?+

Notable localities include Big Rock Quarry, Arkansas, USA; Franklin, New Jersey, USA; Khibiny Massif, Russia.

How much is eggletonite worth?+

Typical asking prices fall in the range of $50-300 per specimen depending on size and quality. Quality, size, and provenance can move individual specimens well outside that range.

What rocks look like eggletonite?+

Eggletonite is most often confused with Friedelite. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with eggletonite?+

Eggletonite commonly co-occurs with Aegirine, Microcline, Pectolite, Analcime. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does eggletonite form in?+

Eggletonite typically forms in nepheline syenite pegmatites, hydrothermal veins. Working float back to the host body is the standard way to chase a fresh occurrence.

What is eggletonite used for?+

Eggletonite is used in collector.

Find eggletonite on the map

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