Rengeite is a rare strontium-zirconium sorosilicate mineral typically found in metamorphic rocks. Collectors prize it for its association with unique geological occurrences in Japan where it forms tabular, dark-colored crystals.

Hardness

5-6

Mohs

Luster

Vitreous

Streak

Brownish Grey

Transparency

Translucent

mineralrarePerrierite Group family

Rengeite

Hardness: 5-6
Luster: Vitreous
Streak: Brownish Grey
Transparency: Translucent

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Is this rengeite?

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 rengeite with a known reference. Rengeite sits at Mohs 5-6 — softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Rengeite leaves a brownish grey streak.
3
Read the luster
Hold the specimen under a strong light. Rengeite typically shows a vitreous luster.
4
Match the color range
Compare against the expected color range: dark brown, black.
5
Look at form & habit
Crystal system: monoclinic. Typical habit: tabular crystals.

Often confused with

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

mineral

Allanite

Mohs 5.5-6

How to tell apart: Streak differs — Rengeite leaves brownish grey, Allanite leaves gray; luster reads vitreous on Rengeite and submetallic on Allanite.

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Often found alongside rengeite

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

All properties

Chemical formula: Sr₄ZrTi₄Si₄O₂₂
Mohs hardness: 5-6
Density: 4.4-4.5 g/cm³
Colors: Dark Brown Black
Streak: Brownish Grey
Luster: Vitreous
Transparency: Translucent
Crystal system: Monoclinic
Crystal habit: Tabular Crystals
Cleavage: None
Rarity: Rare
Uses: Collector
Host rock: Metamorphic Rocks
Typical price: $50-300 per specimen

Where rockhounds find rengeite

Classic worldwide localities

Itoigawa, Niigata Prefecture, Japan

Field-hunting tip

Look in metamorphic rocks country — that is the host setting where rengeite typically forms. If you start seeing titanite, zircon, quartz in float, you are in the right ground. Field specimens usually show a tabular crystals habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify rengeite?+

Mohs hardness is 5-6. It typically shows a vitreous luster. The streak is brownish grey. Common colors include dark brown, black.

Where is rengeite found?+

Notable localities include Itoigawa, Niigata Prefecture, Japan.

How much is rengeite worth?+

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

What rocks look like rengeite?+

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

What minerals are found with rengeite?+

Rengeite commonly co-occurs with Titanite, Zircon, Quartz. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does rengeite form in?+

Rengeite typically forms in metamorphic rocks. Working float back to the host body is the standard way to chase a fresh occurrence.

What is rengeite used for?+

Rengeite is used in collector.

Find rengeite on the map

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