How to identify Fluorite in Quartz

To correctly identify Fluorite in Quartz (CaF2 in SiO2), check each of these features in order. Many rocks and minerals look alike, so cross-reference multiple properties before deciding.

Step-by-step identification

1. 1

   Color

   Overall color and any zoning or banding

   Quartz is typically colorless, white, or milky, but can be various colors (e.g., purple amethyst, yellow citrine, smoky gray). Fluorite exhibits a wide range of colors including purple, green, blue, yellow, pink, and colorless. The combination will show these colors together.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Quartz has a vitreous (glassy) luster. Fluorite also has a vitreous luster.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Crystalline, often with distinct crystal faces for both minerals. Can be massive or granular.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Quartz typically forms hexagonal prisms with pyramidal terminations. Fluorite commonly forms cubic, octahedral, or dodecahedral crystals. The combination will show these forms either intergrown or as inclusions.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Quartz has no cleavage (conchoidal fracture). Fluorite exhibits perfect octahedral cleavage in four directions, which can be observed as flat, shiny surfaces when broken.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Hydrothermal veins, pegmatites, greisens, and as gangue minerals in various metallic ore deposits (e.g., lead-zinc, tin, silver). Often found in granitic and metamorphic terrains.

Key Facts

Hardness

Quartz: 7 on Mohs scale; Fluorite: 4 on Mohs scale. This difference is crucial for identification.

Specific Gravity

Quartz: 2.65 g/cm³; Fluorite: 3.18 g/cm³ (can vary slightly with impurities).

Crystal System

Quartz: Trigonal; Fluorite: Isometric (Cubic).

Color

Variable, as described above, depending on the specific colors of the fluorite and quartz present.

Luster

Vitreous (glassy).

Transparency

Transparent to translucent for both minerals.

Fracture

Quartz: Conchoidal; Fluorite: Subconchoidal to uneven.

Cleavage

Quartz: None; Fluorite: Perfect octahedral (4 directions).

Composition

Quartz: Silicon dioxide (SiO2); Fluorite: Calcium fluoride (CaF2).

Physical characteristics

• Crystal Habit: Quartz: Prismatic, massive, granular; Fluorite: Cubic, octahedral, massive, granular. Often intergrown or as inclusions.
• Cleavage Type: Quartz: None; Fluorite: Perfect octahedral {111}.
• Fracture Type: Quartz: Conchoidal; Fluorite: Subconchoidal to uneven.
• Tenacity: Quartz: Brittle; Fluorite: Brittle.
• Luster Type: Vitreous.

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