Fassinaite is an extremely rare lead thiosulfate mineral that typically occurs as small, tabular crystals. It is primarily found as an alteration product of galena in lead-rich oxidation zones. Due to its rarity and delicate nature, it is highly sought after by advanced systematic mineral collectors.

Hardness

Mohs

Luster

Adamantine

Streak

White

Transparency

Transparent

mineralrare

Fassinaite

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

Is this fassinaite?

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 fassinaite with a known reference. Fassinaite 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. Fassinaite leaves a white streak.
3
Read the luster
Hold the specimen under a strong light. Fassinaite typically shows a adamantine luster.
4
Match the color range
Compare against the expected color range: colorless, white, pale yellow.
5
Look at form & habit
Crystal system: orthorhombic. Typical habit: tabular crystals.

Often confused with

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

How to tell apart: Cerussite is the harder of the two (Mohs 3-3.5 vs. 2).

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Often found alongside fassinaite

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

All properties

Chemical formula: Pb₂S₂O₃
Mohs hardness: 2
Density: 5.68 g/cm³
Colors: Colorless White Pale Yellow
Streak: White
Luster: Adamantine
Transparency: Transparent
Crystal system: Orthorhombic
Crystal habit: Tabular Crystals
Cleavage: Perfect
Rarity: Rare
Uses: Collector
Host rock: Hydrothermal Veins
Typical price: $50-300 per specimen

Where rockhounds find fassinaite

Classic worldwide localities

Fassina quarry, Italy
Laurion, Greece

Field-hunting tip

Look in hydrothermal veins country, the host setting where fassinaite typically forms. If you start seeing galena, cerussite, anglesite 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 fassinaite?+

Mohs hardness is 2. It typically shows a adamantine luster. The streak is white. Common colors include colorless, white, pale yellow.

Where is fassinaite found?+

Notable localities include Fassina quarry, Italy; Laurion, Greece.

How much is fassinaite worth?+

Typical asking prices fall in the range of $50-300 per specimen. Quality, size, and provenance can move individual specimens well outside that range.

Is fassinaite safe to handle?+

It contains toxic constituents. Contains lead; wash hands thoroughly after handling and avoid ingestion or inhalation of dust. Handle with care, avoid grinding or breathing dust, and store separately.

What rocks look like fassinaite?+

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

What minerals are found with fassinaite?+

Fassinaite commonly co-occurs with Galena, Cerussite, Anglesite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does fassinaite form in?+

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

What is fassinaite used for?+

Fassinaite is used in collector.

Find fassinaite on the map

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