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, so 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, 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.