Graeserite is an exceptionally rare arsenic-iron-titanium oxide mineral known primarily from the Binntal region of Switzerland. It typically appears as tiny, black, tabular crystals embedded within mineral-rich pockets of metamorphic dolomitic marble. Due to its scarcity and complex chemistry, it is a highly sought-after prize for advanced mineralogists and systematic collectors.

Hardness

5.5-6

Mohs

Luster

Submetallic

Streak

Black

Transparency

Opaque

mineralrare

Graeserite

Hardness: 5.5-6
Luster: Submetallic
Streak: Black
Transparency: Opaque

Is this graeserite?

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 graeserite with a known reference. Graeserite sits at Mohs 5.5-6 — softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Graeserite leaves a black streak.
3
Read the luster
Hold the specimen under a strong light. Graeserite typically shows a submetallic luster.
4
Match the color range
Compare against the expected color range: black.
5
Look at form & habit
Crystal system: orthorhombic. Typical habit: tabular crystals.

Often confused with

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

mineral

Iron Ore

Mohs 5-6.5

How to tell apart: Streak differs — Graeserite leaves black, Iron Ore leaves reddish-brown to black; luster reads submetallic on Graeserite and metallic to submetallic on Iron Ore.

Often found alongside graeserite

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

All properties

Chemical formula: Fe₄Ti₃As₄O₁₉
Mohs hardness: 5.5-6
Density: 4.95 g/cm³
Colors: Black
Streak: Black
Luster: Submetallic
Transparency: Opaque
Crystal system: Orthorhombic
Crystal habit: Tabular Crystals
Cleavage: None Observed
Rarity: Rare
Uses: Collector
Host rock: Dolomitic Marble in Hydrothermal Veins
Typical price: $200-1000+ for micro-specimens

Where rockhounds find graeserite

Classic worldwide localities

Binntal, Valais, Switzerland

Field-hunting tip

Look in dolomitic marble in hydrothermal veins country — that is the host setting where graeserite typically forms. If you start seeing lengenbachite, realgar, sartorite 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 graeserite?+

Mohs hardness is 5.5-6. It typically shows a submetallic luster. The streak is black. Common colors include black.

Where is graeserite found?+

Notable localities include Binntal, Valais, Switzerland.

How much is graeserite worth?+

Typical asking prices fall in the range of $200-1000+ for micro-specimens. Quality, size, and provenance can move individual specimens well outside that range.

Is graeserite safe to handle?+

It contains toxic constituents. Contains arsenic, a toxic element. Handle with care, avoid creating dust, and wash hands thoroughly after handling. Handle with care, avoid grinding or breathing dust, and store separately.

What rocks look like graeserite?+

Graeserite is most often confused with Iron Ore, Manaccanite. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with graeserite?+

Graeserite commonly co-occurs with Lengenbachite, Realgar, Sartorite, Baumhauerite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does graeserite form in?+

Graeserite typically forms in dolomitic marble in hydrothermal veins. Working float back to the host body is the standard way to chase a fresh occurrence.

What is graeserite used for?+

Graeserite is used in collector.

Find graeserite on the map

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