Rock and Mineral Identification Reference

How to Identify Fluorite: Hardness, Streak, Luster and Tests

Quick answer

Fluorite (mineral): 6 identifying properties, 2 home tests, and how to tell it from Calcite, quoted from geology department and survey sources.

Updated 2026-09-10 · Sources: University of Minnesota Common Minerals

Scratch, streak and acid tests mark the specimen, and some produce sharp fragments or dust. Wear eye protection, work in a ventilated space, keep acid off skin, and never taste a mineral you have not already identified.

How to Identify Fluorite: Hardness, Streak, Luster and Tests — Photo: Robert M. Lavinsky · CC BY-SA 3.0 · source

Found one? Take a photo to identify it.

Download on the App Store

What are the key facts?

Type: Mineral
Mohs hardness: 4 (relatively soft)
Streak: White
Luster: Vitreous luster.
Color: Colorless and transparent when pure; commonly purple, but also yellow, green, white, blue, gray, or black.
Cleavage or fracture: Four directions of perfect cleavage, forming octahedrons; brittle.
Specific gravity: 3.0–3.3

What Fluorite looks like

The properties that identify Fluorite — mohs hardness: 4 (relatively soft); streak: White; luster: Vitreous luster; color: Colorless and transparent when pure; commonly purple, but also yellow, green, white, blue, gray, or black; cleavage or fracture: Four directions of perfect cleavage, forming octahedrons; brittle; specific gravity: 3.0–3.3. Hardness, streak and cleavage are the reliable ones; color alone rarely settles it.

Tests you can do at home

UV-light test: fluorite fluoresces (glows) under ultraviolet light.
Dilute HCl test: fluorite does not react with dilute hydrochloric acid, which distinguishes it from calcite. Safety: As with calcite: dilute hydrochloric acid is corrosive — wear eye protection, work in a ventilated area, and avoid skin contact.

Often confused with

[Calcite](/lookup/rocks-and-minerals/calcite): Fluorite has a hardness of 4 and does not react with acid; calcite has a hardness of 3 and fizzes in acid.

Where it is found in North America

Occurs as a pore-filling mineral in carbonate rocks (limestone, dolomite); historically abundant in the Upper Mississippi River Valley and in Hardin and Pope Counties, Illinois.

How to photograph it for identification

Photograph a fresh, unweathered surface in daylight, then a second shot of any crystal faces or broken edge. Include a coin for scale. If you did a streak test, photograph the streak next to the specimen. The app suggests the likely mineral or rock; confirm with hardness and the tests above before you label it.

FAQ

How hard is Fluorite on the Mohs scale?

4 (relatively soft). A fingernail is about 2.5, a copper coin about 3, a steel knife 5.5 and glass about 5.5, so test against those.

What color streak does Fluorite leave?

White. Rub the specimen on an unglazed porcelain tile; the powder color is the streak, and it is more consistent than the specimen color.

How do I tell Fluorite from Calcite?

Fluorite has a hardness of 4 and does not react with acid; calcite has a hardness of 3 and fizzes in acid.

What is the simplest test for Fluorite?

UV-light test: fluorite fluoresces (glows) under ultraviolet light.

See what's actually under your feet.

Start with a single scan.

Found one? Take a photo to identify it.

Download on the App Store

Sources

University of Minnesota Common Mineralscommonminerals.esci.umn.edu/minerals-f/fluorite
University of Minnesota Common Mineralscommonminerals.esci.umn.edu/minerals-f/calcite-and-aragonite

Compiled by the RockLens editorial team

Every fact on this page is taken from the sources listed above; numbers and prices are copied from the source, and prices name the guide or auction and its date. Research and drafting were assisted by AI, and each claim was then checked against the cited sources. Checked 2026-09-10. We do not buy, sell or grade items; the app identifies what you photograph and points you to these references.