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Herkimer Diamond Quartz refers to exceptionally clear, double-terminated quartz crystals found primarily in and around Herkimer County, New York, USA. These crystals are renowned for their brilliant luster and natural faceting, often resembling cut diamonds, hence the name. A distinguishing feature is the common presence of hydrocarbon inclusions, which can appear as black specks, liquid bubbles (sometimes with mobile gas bubbles), or a brownish tint within the crystal. These inclusions provide valuable insights into the geological conditions of their formation.
How to Identify
- Color
- Colorless to transparent, occasionally with a slight brownish tint due to hydrocarbon inclusions. Black hydrocarbon inclusions are common.
- Luster
- Vitreous (glassy) to sub-adamantine, often exceptionally brilliant.
- Texture
- Smooth, naturally faceted crystal faces.
- Crystal Form
- 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.
- Cleavage
- None. Quartz exhibits conchoidal fracture.
- Geological Environment
- 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.
Quick Check
- Color: Colorless to transparent, sometimes with black or brownish hydrocarbon inclusions.
- Luster: Vitreous to sub-adamantine, very brilliant.
- Streak: White (as with all quartz varieties).
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.
Formation
Herkimer Diamonds are double-terminated quartz crystals that formed in vugs (cavities) within dolostone (a type of sedimentary rock composed primarily of the mineral dolomite). The dolostone, specifically the Little Falls Dolostone, was deposited in a shallow marine environment during the Cambrian period. Over geological time, hydrothermal fluids circulated through the dolostone, dissolving some of the dolomite and creating cavities. Silica-rich solutions then precipitated quartz crystals within these vugs. The characteristic double-termination is a result of the crystals growing freely in these open spaces without attachment to a matrix at one end. The hydrocarbon inclusions, which can range from black solid bitumen to liquid petroleum and gaseous hydrocarbons, were incorporated during the crystal growth process, likely from organic matter present in the surrounding sedimentary rocks that was mobilized by the hydrothermal fluids.
Usage
Primarily used as collector's specimens, in jewelry (often faceted or left in their natural double-terminated form), and occasionally in metaphysical practices due to their clarity and unique formation. They are not typically used in industrial applications where standard quartz is employed, due to their aesthetic value and smaller size.
Age Distribution
Cambrian Period, approximately 500 million years ago
Where to Find
Herkimer County, New York, USA
The primary and namesake locality. Found in numerous mines and collecting sites within the Little Falls Dolostone formation.
Middleville, New York, USA
A well-known specific locality within Herkimer County, famous for producing high-quality Herkimer Diamonds.
Little Falls, New York, USA
Another significant locality in Herkimer County where these crystals are found.
Arizona, USA
Similar double-terminated quartz crystals, sometimes referred to as 'Arizona Herkimers', are found, though they are not true Herkimer Diamonds from New York.
Tibet
Double-terminated quartz crystals with similar characteristics have been found in Tibet, sometimes marketed as 'Tibetan Herkimers'.
Finding Tips
Look for Dolostone Outcrops
Herkimer Diamonds are found in the Little Falls Dolostone. Search for exposures of this rock type, particularly in road cuts, quarries, and stream beds.
Identify Vugs and Cavities
The crystals form in vugs. Look for openings, cracks, and pockets within the dolostone. These can range from small fissures to large caverns.
Tools for Extraction
A rock hammer, chisels, and pry bars are often necessary to break open the dolostone and expose the vugs. Safety glasses are essential.
Screening Material
Many crystals are found loose in the weathered soil and clay surrounding dolostone outcrops. Screening this material can yield numerous specimens.
Hydrocarbon Inclusions
While not always present, the presence of black specks or oily residues can be an indicator of a potential Herkimer Diamond, as these are characteristic inclusions.
Similar Rocks
Standard Quartz Crystal
Quartz (SiO2)
Also known as: Rock Crystal
Arkansas Diamond
Quartz (SiO2)
Also known as: Arkansas Quartz
Pecos Diamond
Quartz (SiO2)
Also known as: Pecos Valley Quartz
Scientific Classification
- Mineral Class
- Silicates
- Group
- Tectosilicates (Quartz Group)
- Crystal System
- Trigonal
- Chemical Formula
- SiO2
- Composition
- Silicon dioxide. May contain various hydrocarbon inclusions (e.g., solid bitumen, liquid petroleum, gaseous hydrocarbons), as well as fluid inclusions (water, brine) and occasionally other mineral inclusions (e.g., pyrite, dolomite).
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