Tilasite is a rare calcium magnesium arsenate fluoride mineral often found in metamorphosed ore deposits. It typically occurs as small, prismatic, yellowish to colorless crystals that can be difficult to distinguish from other similar species without mineralogical testing. It is most famous for its occurrence in the classic mining localities of Långban, Sweden, and the Franklin Mining District in New Jersey.

Hardness

Mohs

Luster

Vitreous

Streak

White

Transparency

Transparent

mineralrare

Tilasite

Hardness: 5
Luster: Vitreous
Streak: White
Transparency: Transparent

Is this tilasite?

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

Often confused with

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

Often found alongside tilasite

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

All properties

Chemical formula: CaMg(AsO₄)F
Mohs hardness: 5
Density: 3.75-3.85 g/cm³
Colors: Yellow Yellowish-brown Colorless White
Streak: White
Luster: Vitreous
Transparency: Transparent
Crystal system: Monoclinic
Crystal habit: Prismatic Crystals, Granular
Cleavage: Poor
Rarity: Rare
Uses: Collector
Host rock: Metamorphosed Iron-manganese Deposits
Typical price: $50-500 depending on quality and locality

Where rockhounds find tilasite

Classic worldwide localities

Långban, Sweden
Franklin, New Jersey, USA
Pioche, Nevada, USA

Field-hunting tip

Look in metamorphosed iron-manganese deposits country — that is the host setting where tilasite typically forms. If you start seeing haematite, barite, willemite in float, you are in the right ground. Field specimens usually show a prismatic crystals, granular habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify tilasite?+

Mohs hardness is 5. It typically shows a vitreous luster. The streak is white. Common colors include yellow, yellowish-brown, colorless, white.

Where is tilasite found?+

Notable localities include Långban, Sweden; Franklin, New Jersey, USA; Pioche, Nevada, USA.

How much is tilasite worth?+

Typical asking prices fall in the range of $50-500 depending on quality and locality. Quality, size, and provenance can move individual specimens well outside that range.

Is tilasite safe to handle?+

It contains toxic constituents. Contains arsenic, a toxic element. Wash hands thoroughly after handling and avoid inhaling dust if breaking specimens. Handle with care, avoid grinding or breathing dust, and store separately.

What rocks look like tilasite?+

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

What minerals are found with tilasite?+

Tilasite commonly co-occurs with haematite, barite, willemite, calcite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does tilasite form in?+

Tilasite typically forms in metamorphosed iron-manganese deposits. Working float back to the host body is the standard way to chase a fresh occurrence.

What is tilasite used for?+

Tilasite is used in collector.

Find tilasite on the map

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