How to identify Herkimer Diamond Quartz

To correctly identify Herkimer Diamond Quartz (Quartz (SiO2) with hydrocarbon inclusions), 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

   Colorless to transparent, occasionally with a slight brownish tint due to hydrocarbon inclusions. Black hydrocarbon inclusions are common.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Vitreous (glassy) to sub-adamantine, often exceptionally brilliant.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Smooth, naturally faceted crystal faces.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Distinctive double-terminated hexagonal prisms. This means the crystal has natural facets at both ends, unlike most quartz crystals which are typically terminated at one end and attached to a matrix at the other. The faces are typically well-formed and sharp.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   None. Quartz exhibits conchoidal fracture.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Found in vugs and cavities within dolostone formations, specifically the Little Falls Dolostone in New York. They are often extracted from weathered dolostone or directly from the rock matrix.

Key Facts

Hardness

7 on the Mohs scale

Specific Gravity

2.65 g/cm³

Crystal System

Trigonal

Color

Colorless, transparent; may contain black or brownish hydrocarbon inclusions.

Luster

Vitreous (glassy) to sub-adamantine.

Transparency

Transparent to translucent.

Fracture

Conchoidal (shell-like, curved breaks).

Cleavage

None.

Composition

Silicon dioxide (SiO2) with hydrocarbon inclusions.

Physical characteristics

• Crystal Habit: Double-terminated hexagonal prisms, often with well-developed faces and sharp edges. Can occur as single crystals or in clusters.
• Cleavage Type: Absent.
• Fracture Type: Conchoidal.
• Tenacity: Brittle.
• Luster Type: Vitreous to sub-adamantine.

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