Marchettiite is an extremely rare organic mineral found in volcanic fumaroles. It typically appears as small, yellowish tabular crystals formed by the reaction of volcanic gases with biological matter.

Hardness

Mohs

Luster

Vitreous

Streak

White

Transparency

Transparent

mineralrare

Marchettiite

Hardness: 2
Luster: Vitreous
Streak: White
Transparency: Transparent

Is this marchettiite?

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

Often confused with

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

Often found alongside marchettiite

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

All properties

Chemical formula: Na(C₄H₃N₂O₃)·H₂O
Mohs hardness: 2
Density: 1.74 g/cm³
Colors: Yellow Brownish-yellow
Streak: White
Luster: Vitreous
Transparency: Transparent
Crystal system: Monoclinic
Crystal habit: Tabular Crystals
Cleavage: None
Rarity: Rare
Uses: Collector
Host rock: Fumarole Deposits
Typical price: $100-500 depending on specimen quality

Where rockhounds find marchettiite

Classic worldwide localities

Monte Somma, Italy

Field-hunting tip

Look in fumarole deposits country — that is the host setting where marchettiite typically forms. If you start seeing oxammite, tschermigite 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 marchettiite?+

Mohs hardness is 2. It typically shows a vitreous luster. The streak is white. Common colors include yellow, brownish-yellow.

Where is marchettiite found?+

Notable localities include Monte Somma, Italy.

How much is marchettiite worth?+

Typical asking prices fall in the range of $100-500 depending on specimen quality. Quality, size, and provenance can move individual specimens well outside that range.

What rocks look like marchettiite?+

Marchettiite is most often confused with Oxammite. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with marchettiite?+

Marchettiite commonly co-occurs with Oxammite, Tschermigite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does marchettiite form in?+

Marchettiite typically forms in fumarole deposits. Working float back to the host body is the standard way to chase a fresh occurrence.

What is marchettiite used for?+

Marchettiite is used in collector.

Find marchettiite on the map

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