How to identify Polished Stone

To correctly identify Polished Stone (Unknown Polished Stone), 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

   Highly variable, depends on the original rock/mineral. Can be any color or combination of colors.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Typically vitreous (glassy), resinous, waxy, or silky, depending on the original material and the quality of the polish. The polishing process enhances the natural luster.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Smooth, often cool to the touch, with no rough edges or sharp points. The surface should feel uniform.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Not applicable to the 'polished' state itself. The original rock/mineral may have had a specific crystal form, but polishing often obscures or removes external crystal faces, presenting a rounded or shaped form.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Cleavage planes, if present in the original mineral, may be visible as internal lines or planes, but the external surface will be smooth and polished, not exhibiting cleavage breaks.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Not applicable to the 'polished' state. The geological environment is determined by the formation of the original rock or mineral, which can be igneous, sedimentary, or metamorphic.

Key Facts

Hardness

Variable, depends on the original rock/mineral (e.g., Quartz: 7, Calcite: 3, Feldspar: 6-6.5 on Mohs scale)

Specific Gravity

Variable, depends on the original rock/mineral (e.g., Quartz: 2.65, Calcite: 2.71, Obsidian: 2.3-2.6)

Crystal System

Variable, depends on the original mineral (e.g., Quartz: Hexagonal, Calcite: Trigonal, Feldspar: Monoclinic/Triclinic)

Color

Highly variable, encompasses all colors and patterns found in natural rocks and minerals.

Luster

Enhanced by polishing; typically vitreous, resinous, waxy, or silky.

Transparency

Variable, can be opaque, translucent, or transparent depending on the original material.

Fracture

Variable, depends on the original rock/mineral (e.g., Conchoidal for quartz and obsidian, uneven for many rocks). Polishing does not alter the internal fracture characteristics.

Cleavage

Variable, depends on the original mineral. Cleavage planes may be present internally but the polished surface will be smooth.

Composition

Variable, depends on the original rock/mineral (e.g., SiO2 for quartz, CaCO3 for calcite, complex silicates for feldspars).

Physical characteristics

• Crystal Habit: Not applicable to the polished state; refers to the original mineral's growth form.
• Cleavage Type: Variable, depends on the original mineral (e.g., perfect, good, poor, none).
• Fracture Type: Variable, depends on the original rock/mineral (e.g., conchoidal, uneven, splintery).
• Tenacity: Variable, depends on the original rock/mineral (e.g., brittle, tough).
• Luster Type: Enhanced by polishing; typically vitreous (glassy), resinous, waxy, or silky.

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