Yoderite is an exceptionally rare metamorphic silicate mineral primarily known from the Mautia Hill locality in Tanzania. It typically appears as deep violet to purple tabular crystals embedded within kyanite-bearing schists and is highly sought after by advanced mineral collectors.

Hardness

Mohs

Luster

Vitreous

Streak

White

Transparency

Transparent

mineralrare

Yoderite

Hardness: 6
Luster: Vitreous
Streak: White
Transparency: Transparent

Is this yoderite?

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 yoderite with a known reference. Yoderite sits at Mohs 6, softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Streak: white.
3
Read the luster
Hold the specimen under a strong light. Luster: vitreous.
4
Match the color range
Compare against the expected color range: purple red, deep blue, emerald green, yellow.
5
Look at form & habit
Crystal system: monoclinic. Typical habit: anhedral grains, lath.

Often confused with

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

How to tell apart: Staurolite is the harder of the two (Mohs 7-7.5 vs. 6); luster reads vitreous on Yoderite and subvitreous to resinous on Staurolite.

Compare →

Often found alongside yoderite

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

All properties

Chemical formula: (Mg,Al)₆Si₄O₁₂(OH)₂
Mohs hardness: 6
Density: 3.39 g/cm³
Colors: Purple red Deep blue Emerald green Yellow
Streak: White
Luster: Vitreous
Transparency: Transparent
Crystal system: Monoclinic
Crystal habit: Anhedral grains, lath
Cleavage: Partings [001], good and {100}, poor
Rarity: Rare
Uses: Collector
Host rock: A major phase in quartz-kyanite-talc schist formed under conditions of ~10 kbar H2O pressure and 800 ° C

Where rockhounds find yoderite

Classic worldwide localities

Mautia Hill, Kongwa, Central Province, Tanzania

Field-hunting tip

Where it forms: A major phase in quartz-kyanite-talc schist formed under conditions of ~10 kbar H2O pressure and 800 ° C. If you start seeing kyanite, talc, hematite in float, you are in the right ground. Typical habit: anhedral grains, lath. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify yoderite?+

Mohs hardness is 6. Luster: vitreous. The streak is white. Common colors include purple red, deep blue, emerald green, yellow.

Where is yoderite found?+

Notable localities include Mautia Hill, Kongwa, Central Province, Tanzania.

What rocks look like yoderite?+

Yoderite is most often confused with Kyanite, Staurolite. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with yoderite?+

Yoderite commonly co-occurs with Kyanite, Talc, Hematite, Quartz. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does yoderite form in?+

Where it forms: A major phase in quartz-kyanite-talc schist formed under conditions of ~10 kbar H2O pressure and 800 ° C. Working float back to the host body is the standard way to chase a fresh occurrence.

What is yoderite used for?+

Yoderite is used in collector.

Find yoderite on the map

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