The Herkimer Diamond Mining Glossary
An in-progress reference guide to local terminology used by Herkimer Diamond miners and collectors in the Mohawk Valley region of Upstate New York.
This glossary documents the colloquial language of the Herkimer mining community. Many terms represent local usage that may differ from formal geological or mineralogical definitions. Where applicable, locality-specific meanings are noted alongside their broader scientific context.
Please Note: This glossary is intended to document regional terminology and facilitate communication among collectors, rather than to redefine established scientific nomenclature.
Herkimer Diamond & Herkimer-style quartz
Herkimer Diamond
Originally defined a double-terminated quartz crystal with exceptional clarity and luster, found within Herkimer County, New York. Usage has broadened in the market, with the term often being used synonymously with "Herkimer-style quartz."
Herkimer-style quartz
A variety of quartz characterized by transparent, double-terminated crystals with high luster and clarity. Formed in relatively low temperature environments in sedimentary rocks. Often associated with hydrocarbons and may include petroleum inclusions. Found in New York and analogous deposits worldwide. (mindat)
For the purposes of this glossary, all mentions of "Herkimer Diamond" or "Herkimer-style quartz" will be in reference to the quartz crystals found in Herkimer County AND surrounding areas, as this glossary encompasses the regional terms used by the local industry.
Mining & "Geology" Terms
Little Falls Dolostone
The geologic unit in which Herkimer Diamonds are found. A Late Cambrian age dolostone (with some sandstone) of the Mohawk Valley. (Zenger 1976)
Ledge
The in-place (in situ) bedrock from which Herkimer Diamonds are mined. Locally, this refers to the Little Falls Dolostone. (Pictured below: two people looking at the "ledge" at the Herkimer Diamond Mine)
Pocket
A larger void within the Little Falls Dolostone, often lined with mud or hydrocarbon residue. Pockets can host crystal clusters, loose crystals, and pocket clay.
Vug
Smaller, irregular openings in the dolostone, commonly coated in black anthraxolite (pyrobitumen). May or may not contain Herkimer-style quartz; often hosts druzy quartz, dolomite, and/or calcite. (Pictured below: a Herkimer Diamond in a anthraxolite-coated vug)
Pocket layer
The stratigraphic interval(s) of dolostone where larger pockets are commonly found. Commercial miners actively target these layers.
Gemmy layer
A layer or layers of vuggy dolostone where high-clarity (gemmy) crystals are prevalent. Typically yields smaller but exceptionally clear crystals. (Pictured below: mud-coated Herkimer Diamonds peeking out from the top of the gemmy layer)
Tailings
Rocks that have been removed from the ledge and discarded.
Mining Methods & Tools
Shims
Homemade tools made out of old car leaf springs that are cut and grinded down. Used to expand cracks in the ledge.
Pry bar (or Crowbar)
Tool lifting or moving larger pieces or sections of the ledge.
Sledgehammer
Hammer used break apart pieces of dolostone and to drive wedges into larger sections of ledge.
Screening
Sifting through dirt and smaller tailings using metal screens to find smaller crystals.
Surface find
A crystal found loose on the surface rather than mined from the ledge.
Fee dig (or Pay-to-dig)
Sites where visitors pay to mine for Herkimer Diamonds; e.g., Herkimer Diamond Mines, Ace of Diamonds.
Size & Quality Descriptors
Micros
Tiny Herkimer Diamonds ranging in size from nearly microscopic to a few millimeters. (Pictured below: Herkimer Diamond micros, ranging from 2-3 mm in size)
Gemmies
Smaller, high-clarity Herkimer Diamonds with excellent luster; ranging from a few millimeters marble-sized.
Palmer
A Herkimer-style quartz approximately the size of one's palm. Used colloquially for "nice hand-sized" crystals.
Goonie
A Herkimer-style quartz specimen larger than one's palm; often bulky or blocky and prized for size rather than perfection.
Mohawk Monster
Name given to exceptionally large Herkimer-style quartz specimens from the Mohawk Valley region.
Crystal Habits & Forms
Double-terminated (or DT)
A crystal with natural terminations (points) on both ends; characteristic of Herkimer Diamonds.
Equant
Approximately equal dimensions in all directions.
Tabular (or Tabby)
Flattened crystal form; wider than it is tall.
Scepter
A crystal with a larger termination sitting atop a smaller "handle"; rare overall, though more prevalent in the Little Falls mines.
Floater
A crystal that appears to have formed freely in a pocket without attachment to the matrix; shows no contact marks.
Faces (or Crystal faces)
The flat, external surfaces of a crystal bounded by edges.
Termination
The naturally formed point or tip of a crystal.
Crystal Features & Inclusions
Cluster
A group two or more of crystals grown together, which may include riders and sidecars. (Pictured below: a cluster of two water-clear Herkimer Diamonds)
Sidecar
A smaller quartz crystal attached to and in parallel growth with a larger Herkimer-style quartz.
Rider
A smaller quartz crystal perched on a larger crystal, often off-axis. Distinct from a sidecar.
Contacts (or Contact indentations)
Areas of bumpy/rounded roughness on a crystal where it grew in contact with the dolostone. Contacts are not damage; they record natural growth. (Pictured below: contact indentations on a Herkimer Diamond)
Footprint
Geometric imprints left behind where another crystal was previously attached. Synonym: key.
Key
Geometric imprints left behind where another crystal was previously attached. Synonym: footprint.
Reconstructed
Describes a Herkimer Diamond cluster reassembled along original footprints and keys. A common practice in specimen preparation; though it should always be disclosed by vendors.
Negative inclusion
An internal void enclosed within a crystal, often mimicking external crystal forms (e.g., tiny double-terminated cavities). (Pictured below: clear Herkimer Diamond with negative inclusions circled in pink)
Rainbow (or Iris)
Internal fractures that create rainbow-like light diffraction. Pictured below.
Phantom
A ghost-like outline of an earlier growth stage visible inside the crystal. Usually due to pyrobitumen inclusions or dissemination in Herkimer Diamonds. (Pictured below: Herkimer Diamond with phantom near upper termination)
Enhydro (or Enhydrous crystal)
A crystal containing a trapped bubble of liquid (often water) that moves when tilted.
Matrix
The fine-grained material in which a larger-grained material is embedded, for sedimentary rocks. Colloquially used in reference specifically to a piece of dolostone with a Herkimer Diamond attached. (Pictured below: a Herkimer Diamond matrix specimen)
Associated Minerals/Mineraloids
Pyrobitumen
A black hydrocarbon mineraloid formed through the polymerization of petroleum over geologic time. Synonym: anthraxolite. (mindat)
Anthraxolite
A black hydrocarbon mineraloid formed through the polymerization of petroleum over geologic time. Synonym: pyrobitumen. (mindat)
Druzy (also spelled Drusy or Druse)
A coating of tiny crystals, often quartz, lining vug walls. (Pictured below: druzy quartz crystals on dolostone)
Dolomite
The dominant rock-forming mineral of dolostone. Found crystallized in pockets and vugs as rhombohedral crystals, often with a distinct "saddle-shape." Usually tan to pink in color.
Calcite
The dominant rock-forming mineral of limestone. Found crystallized in pockets and vugs in the Little Falls dolostone; tends to have a dull luster on crystal faces, and a waxy to vitreous luster on cleaved faces. Usually opaque white to slightly transparent white in the Little Falls dolostone.
References:
Zenger, D.H. (1976). Definition of Type Little Falls Dolostone (Late Cambrian),
East-Central New York. Geologic Notes.
Mindat.org - Mineralogical database (Referenced for: Herkimer-style quartz, pyrobitumen, and anthraxolite)