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

5-5.5

Mohs

Luster

Adamantine

Streak

Pale greenish brown

Transparency

Transparent

mineralrarePerrierite Group family

Rengeite

Hardness: 5-5.5
Luster: Adamantine
Streak: Pale greenish brown
Transparency: Transparent

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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 5-5.5, softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Streak: pale greenish brown.
3
Read the luster
Hold the specimen under a strong light. Luster: adamantine.
4
Match the color range
Compare against the expected color range: dark greenish brown.
5
Look at form & habit
Crystal system: monoclinic. Typical habit: anhedral grains, microscopic 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 pale greenish brown, Allanite leaves gray; luster reads adamantine 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: 5-5.5
Density: 4.12 g/cm³
Colors: Dark greenish brown
Streak: Pale greenish brown
Luster: Adamantine
Transparency: Transparent
Crystal system: Monoclinic
Crystal habit: Anhedral grains, microscopic crystals
Cleavage: None
Rarity: Rare
Uses: Collector
Host rock: In jade pebbles from rocks in a high P/T metamorphic belt as tectonic inclusions in serpentinite melange

Where rockhounds find rengeite

Classic worldwide localities

Oyashirazu shore, Sea of Japan, Ohmi Town
Beds of the Kotakigawa and Himekawa rivers, Itoigawa City, Ohmi region, Niigata Prefecture, Japan

Field-hunting tip

Where it forms: In jade pebbles from rocks in a high P/T metamorphic belt as tectonic inclusions in serpentinite melange. If you start seeing jadeite, natrolite, rutile in float, you are in the right ground. Typical habit: anhedral grains, microscopic crystals. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify rengeite?+

Mohs hardness is 5-5.5. Luster: adamantine. The streak is pale greenish brown. Common colors include dark greenish brown.

Where is rengeite found?+

Notable localities include Oyashirazu shore, Sea of Japan, Ohmi Town; Beds of the Kotakigawa and Himekawa rivers, Itoigawa City, Ohmi region, Niigata Prefecture, Japan.

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 Jadeite, Natrolite, Rutile, Titanite, Pectolite, Itoigawaite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does rengeite form in?+

Where it forms: In jade pebbles from rocks in a high P/T metamorphic belt as tectonic inclusions in serpentinite melange. 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.