How to identify Rubellite in Quartz

To correctly identify Rubellite in Quartz (Rubellite (a variety of Tourmaline) in Quartz), 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

   The rubellite inclusions are typically pink, red, or purplish-red. The quartz matrix is usually colorless, white, or smoky.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Vitreous (glassy) for both rubellite and quartz.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Can range from smooth (polished) to rough (natural crystal faces). The rubellite inclusions may appear as fine needles, fibrous aggregates, or distinct prismatic crystals within the quartz.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Rubellite typically forms as prismatic crystals with characteristic striations parallel to the c-axis, often with a triangular cross-section. Quartz forms hexagonal prisms terminating in hexagonal pyramids. Inclusions can be acicular, fibrous, or blocky.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Quartz has no true cleavage, exhibiting conchoidal fracture. Rubellite has poor to indistinct cleavage parallel to the c-axis.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Primarily found in granitic pegmatites, which are late-stage differentiates of granitic magmas. Also found in some hydrothermal veins and metamorphic rocks, though pegmatites are the most common source for gem-quality material.

Key Facts

Hardness

7 (Quartz) to 7-7.5 (Rubellite) on the Mohs scale

Specific Gravity

2.65 (Quartz) to 3.02-3.26 (Rubellite)

Crystal System

Trigonal (Quartz) and Trigonal (Rubellite)

Color

Pink, red, purplish-red inclusions in colorless, white, or smoky matrix

Luster

Vitreous

Transparency

Transparent to translucent

Fracture

Conchoidal (Quartz), Uneven to conchoidal (Rubellite)

Cleavage

None (Quartz), Indistinct (Rubellite)

Composition

SiO2 (Quartz) and Complex borosilicate of aluminum with iron, magnesium, and other elements, specifically rich in manganese and lithium for rubellite (Tourmaline Group)

Physical characteristics

• Crystal Habit: Quartz: Prismatic hexagonal crystals, massive. Rubellite: Prismatic, acicular, fibrous, radiating aggregates within quartz.
• Cleavage Type: Quartz: None. Rubellite: Poor to indistinct on {1011} and {0001}.
• Fracture Type: Quartz: Conchoidal. Rubellite: Uneven to conchoidal.
• Tenacity: Brittle
• Luster Type: Vitreous

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