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, so 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, 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.