Herkimer Diamonds: The Complete Guide
History, geology, identification, where to dig, and real specimens from New York’s Mohawk Valley, all in one place. Herkimer diamonds aren’t diamonds at all. They’re some of the clearest natural quartz crystals on Earth.
Quick facts
The name and the history
Herkimer diamonds are named after Herkimer County, New York. The county was formed in 1791 and named after General Nicholas Herkimer, a local militia leader who was mortally wounded at the Battle of Oriskany in 1777 during the Revolutionary War. The crystals picked up his name because the richest outcrops sat in his county.
- 1777Nicholas Herkimer leads the Tryon County militia at the Battle of Oriskany and dies of his wounds days later. His home near Little Falls is now the Herkimer Home State Historic Site.
- 1791Herkimer County is created from part of Montgomery County and named in his honor.
- Late 1700sWorkmen cutting into the Mohawk Valley dolomite find the crystals in large quantities. Their clarity and natural facets earn them the name “diamonds.”
- 1819The first scientific notes on New York’s clear quartz appear. In a letter published in Benjamin Silliman’s American Journal of Science, Professor Chester Dewey describes a crystal with a partly filled liquid cavity holding floating black particles, the same inclusions Herkimers are known for. His specimen came from the Catskill region, not Herkimer County.
- 1823James Hadley, writing in the New York Medical and Physical Journal, describes “limpid quartz” in Herkimer County along West Canada Creek near where it meets the Mohawk River. This is one of the earliest written records from the Herkimer district itself.
- 1837James Dwight Dana’s System of Mineralogy, the standard American reference, notes that “several hundred crystals are often obtained from a single cavity,” with crystals up to four to six inches long.
- 1842Lewis C. Beck’s Mineralogy of New York, part of the state’s first geological survey, documents the region’s quartz localities.
- 1876–1901Collector A. B. Crim of Herkimer County starts collecting in 1876 and selling by 1878. At the 1893 World’s Columbian Exposition in Chicago, his display wins the highest award and reportedly sells more than 30,000 crystals. He takes the top medal again at the 1901 Pan-American Exposition in Buffalo, making “Herkimer diamonds” a nationally known souvenir.
- 1896–1905Scientists study the district: A. P. Coleman describes the black carbon mineral anthraxolite (1896), and H. P. Cushing maps the geology around Little Falls (1905).
- 20th centuryPay-to-dig mines open near Middleville and elsewhere. Anyone can rent tools, split rock, and keep what they find.
- 2009–2017Bills to make the Herkimer diamond New York’s official state mineral pass the State Senate several times, including in 2015, but the Assembly never acts on them. It is still not an official symbol.
- TodaySeveral fee-dig mines operate each season, and researchers are still testing new ideas about how the crystals formed.
How Herkimer diamonds form
Most quartz grows attached to a rock wall, so it only gets one point. Herkimers grew suspended in pockets inside the dolomite, which let them form points on both ends with brilliant, naturally polished faces.
- The birthplace. Late Cambrian sea-floor sediment hardens into limestone and is altered to dolomite, the Little Falls Dolostone.
- Pockets open. Acidic fluids dissolve cavities (vugs) inside the dolomite, giving crystals room to grow.
- Fluids arrive. Faults and fractures carry deep fluids, including hydrocarbons, into the pockets.
- Seeds form. In one leading explanation, millions of tiny quartz crystals and “crystal frost” form first and act as seeds for the larger ones.
- Slow, clean growth. Quartz grows very slowly in a protected space, producing exceptional clarity and sharp faces.
- Color and inclusions. Oil can be trapped as black hydrocarbon specks or fluid bubbles. Radioactive elements carried with the hydrocarbons can turn some crystals smoky.
- Uncovered. Ice Age glaciers and later erosion strip away overlying rock, leaving the crystal-bearing dolomite close enough to the surface to dig.
Why do mines differ? According to HerkimerHistory.com, differences come from how intense the mineral-forming events were and how much fluid flowed vertically versus horizontally at each site, including how close it is to major faults.
Inside the crystal: the science
Herkimers are some of the most studied quartz crystals in North America because they preserve small samples of the fluids they grew from.
Two kinds of inclusions
Primary inclusions were trapped while the crystal was growing and record the original pocket fluid: salty water, petroleum, and gas, mostly carbon dioxide. Some hold two or three phases at once, such as liquid plus a gas bubble plus a solid. Secondary inclusions formed later, when a crack in the crystal healed and sealed fluid inside, often as flat, feathery planes. For more on how scientists read these, see our post on inclusions.
Where the ingredients came from
- Silica: likely from sponge spicules and other silica in the surrounding sediments, dissolved and reprecipitated as quartz.
- Black carbon: the anthraxolite (pyrobitumen) is biogenic, meaning it derives from the remains of ancient organisms, the same source as petroleum.
- Tiny mineral guests: calcite, dolomite, pyrite, and sphalerite have all been found as inclusions or companions.
Why they’re so clear
Low temperature, slow growth, and a protected pocket let quartz add layer after layer with very few defects. HerkimerHistory.com sums it up: clear, sharp crystals need room to grow free of impurities and protection from natural stresses after they form.
Properties at a glance
| Chemistry | SiO2 (silicon dioxide) | Crystal system | Trigonal (hexagonal-looking) |
|---|---|---|---|
| Hardness | 7 | Specific gravity | 2.6–2.7 |
| Luster | Vitreous (glassy) | Break | Conchoidal fracture, no cleavage |
| Color | Colorless to smoky, golden when stained | Refractive index | About 1.54–1.55 (quartz) |
Research deep dive: open questions and new findings
Two centuries after the first written descriptions, geologists still don’t fully agree on how Herkimer diamonds formed. Here’s where the research stands, including the parts that are still being argued.
1. A fossilized oil field
The most striking idea in recent Herkimer research is that the mining district is essentially a fossil oil deposit. Dr. W. David Hoisington’s field survey of the district puts it simply: where there are Herkimer diamonds, there is also hydrocarbon. He documents black hydrocarbon filling dolomite-lined vugs, coating early dolomite crystals, lining fractures, and migrating vertically across bedding layers. He also describes an ancient karst feature (a buried sinkhole) with hydrocarbon scattered through weathered rock, which shows the oil arrived long after the rock formed rather than growing in place with it. Pockets that hold both hydrocarbon and quartz often produce the clearest crystals.
2. Can quartz even grow in oil?
For decades, petroleum geologists assumed oil shut down quartz growth, because oil coats grain surfaces and pushes water out. A 2004 lab study in Geochimica et Cosmochimica Acta tested that by growing quartz in autoclaves at water-to-oil ratios from pure water to pure oil. Quartz kept growing and kept trapping both oil and water inclusions even at high oil saturation. Up to 250 °C, the trapped oil still matched the original fluid; at 350 °C it began cracking into methane. That’s direct experimental support for the idea that Herkimers grew in an oily brine. Earlier work points the same way: Bennett and Siegel (1987) showed organic molecules can greatly increase how much silica water can carry, and Chamberlain (1988) proposed exactly that mechanism for slow, low-temperature Herkimer growth.
3. The temperature debate
The “warm bath” camp
Classic fluid-inclusion work (Roedder, 1979; Ulrich, 1989) puts growth at roughly 50 °C, only about 1 km down. Low heat plus slow growth is a tidy explanation for the extreme clarity.
The “hot oil” camp
HerkimerHistory.com argues for roughly 200 to 250 °C, a range typical of petroleum-bearing basin fluids. Deep burial under several kilometers of now-eroded sediment would make higher temperatures plausible.
Why the gap? Fluid inclusions record the conditions at the moment they were sealed, and roughly three in four Herkimers have healed cracks full of later fluids. Which inclusions get measured can change the answer. It’s still an open question.
4. When: the Appalachian squeeze
The Herkimer quartz has never been dated directly. Its Carboniferous age comes from the order in which minerals formed, not from a radiometric clock. The best clue is regional. In a 1985 paper in Science, USGS geologists P. P. Hearn and J. F. Sutter dated feldspar that grew inside Cambrian carbonates in western Maryland to the Late Pennsylvanian to Early Permian, and concluded that hot brines were squeezed across the whole Appalachian basin when the mountains were pushed up during the Alleghanian orogeny, the collision that assembled Pangaea. A 2002 review of dated ore deposits by David Leach, cited by HerkimerHistory.com, found more than 75% fall between the Devonian and Permian. Herkimers fit neatly into that same window of basin-wide fluid flow.
5. Where did the oil come from?
Ulrich (1989) suggested the black carbon came from the algal stromatolites fossilized in the Little Falls Dolostone itself, meaning the rock made its own oil. Hoisington’s work pushes back: hydrocarbon that crosses bedding layers and fills later karst and fractures suggests it migrated in from elsewhere, in several pulses. Two distinct forms of anthraxolite in the rock also point to at least two separate episodes of mineralization.
6. Can a lab tell a Herkimer from a “Pakimer”?
Surprisingly, not reliably. A 2018 gemology study at the Université de Nantes compared Herkimer and Pakistani double-terminated quartz using microscopy, UV, FTIR, and micro-Raman spectroscopy. Both contained black hydrocarbon inclusions and negative crystals, and both glowed blue under UV, though the Pakistani stones glowed much more strongly under shortwave. The Pakistani samples also held yellow oil inclusions with a distinct infrared signature. The author’s conclusion: no feature consistently separates the two localities. That’s why a documented New York locality matters so much when buying.
7. Why skeletal Herkimers exist
Every deposit in the district produces skeletal and hopper crystals. They form when a crystal grows fast enough that its edges outrun its faces, leaving stepped or hollow faces. That happens when silica in the fluid spikes well above saturation. Researchers link those spikes to evaporation or pressure changes in the pocket, with hydrocarbons likely playing a role. A skeletal Herkimer is essentially a snapshot of a fast, chaotic growth episode in an otherwise slow system.
8. Researchers are trying to grow them
According to HerkimerHistory.com, lab work at Kingston University in the UK has tried to grow quartz in the presence of hydrocarbons to reproduce Herkimer-style crystals. If it works, it would be the strongest test yet of the oil-and-seed-crystal model.
Fun fact: Herkimers in your vodka
Herkimers have a second career in spirits. Dan Aykroyd’s Crystal Head Vodka, launched in 2007, passes its final three filtrations through layers of Herkimer diamonds.
Types you’ll see
Water-clear
The classic: transparent, double-terminated, and bright enough to pass for a cut gem.
Smoky and black
Darkened by natural radiation and heavy hydrocarbon inclusions. Black Herkimers are prized.
Golden
Warm yellow to honey color, usually from iron-bearing coatings or stains on and in the crystal.
Skeletal and window
Stepped, hollowed, or framed faces that grew fast along the edges. Uncommon and very collectible.
Clusters and on matrix
Groups grown together, or crystals still sitting on the original dolomite, which proves the context.
Druzy
Glittering carpets of tiny crystals lining the pocket walls.
Enhydro and included
Trapped pockets of fluid (sometimes with a moving bubble), black hydrocarbon specks, or smaller crystals sealed inside.
Herkimer vs. the look-alikes
Plenty of clear, double-pointed crystals are sold as “Herkimer.” Here’s how the real thing stacks up.
| Property | Herkimer diamond | Other double-terminated quartz (“Pakimer” etc.) | Polished quartz point | Glass |
|---|---|---|---|---|
| Origin | Mohawk Valley, NY only | Pakistan, China, and elsewhere | Any quartz, cut to shape | Factory made |
| Points | Natural, both ends | Natural, both ends | Ground and polished | Molded or cut |
| Faces | Bright, with fine natural growth marks | Often more frosted or etched | Perfectly flat, rounded edges | Smooth, may show mold seams |
| Inside | Black hydrocarbon specks, fluid bubbles | Varies, often cloudy or included | Whatever the source quartz had | Round gas bubbles, swirl lines |
| Hardness | 7, scratches glass | 7 | 7 | About 5.5, scratched by quartz |
| Red flag | — | Sold as “Herkimer” without a NY locality | Sold as natural | Perfect, cheap, and in bulk |
Not sure about a crystal you already own? Try the checker below.
Myths vs. facts
A lot of what’s repeated about Herkimers online is half-true. Here’s what the sources actually support.
Myth: The Herkimer diamond is New York’s official state mineral.
Fact: Not yet. Bills to name it the state mineral have passed the State Senate several times, including S.5866 in 2015, but the Assembly never acted on them. New York’s official state gem is garnet, adopted in 1969.
Myth: The crystals are 500 million years old.
Fact: The host rock is about 500 million years old. The quartz grew later, and is generally interpreted as Carboniferous, roughly 300 to 360 million years ago.
Myth: “Mohawk” means “People of the Crystals.”
Fact: The Mohawk name for themselves, Kanienʼkehá꞉ka, is usually translated as “People of the Flint.” A “crystal” reading has been suggested by some local writers, but it isn’t the standard translation. Some guides say Native people and early settlers used the crystals as amulets and trade items, but mineral historian Frank Festa notes there is no documented archaeological evidence of pre-European collecting, though it is possible.
Myth: They formed in scorching heat deep in the Earth.
Fact: Fluid-inclusion work points to surprisingly gentle conditions, around 51 °C and about a kilometer down. The slow, cool growth is part of why they’re so clear.
Myth: Any clear double-pointed quartz is a Herkimer.
Fact: The name is tied to the Mohawk Valley. Similar crystals from Pakistan, China, Arizona, and elsewhere are “Herkimer-type” or “Herkimer-style” at best. Pakistan’s version, often with golden petroleum inclusions that glow blue under UV, is sold as “Pakimer.”
Myth: Herkimers are the only New York “diamonds.”
Fact: Clear quartz earned the nickname across the state. Lake George has a Diamond Island, and early 1800s accounts describe local people collecting crystals there to sell. Herkimer’s are simply the most famous.
Real Herkimer or not? Quick checker
Tick everything that matches the crystal in front of you. This is a guide, not a lab test, but it catches the most common look-alikes: glass, polished quartz points, and double-terminated quartz from other countries sold as “Herkimer.”
Good signs
Warning signs
Where they’re found and where to dig
Herkimer diamonds come from a stretch of the Mohawk Valley roughly 40 miles long, where the Little Falls Dolostone reaches the surface. Several fee-dig mines let you pay for the day and keep what you find. Seasons usually run from spring into mid-fall, so check each mine’s site for current hours, fees, and rules before you go.
Middleville / Herkimer
Herkimer County- Herkimer Diamond Mines: the best-known public mine, on Route 28, with a shop and a campground nearby.
- Ace of Diamonds Mine & Campground: a classic dig. Mindat records enhydro quartz and pyrobitumen here.
Little Falls
Herkimer County- Diamond Mountain Mining: collector-focused, with reservation and wilderness digs.
- Also home to Erie Canal Lock 17 and the Herkimer Home State Historic Site.
St. Johnsville
Montgomery County- Crystal Grove Diamond Mine: known for crystals on matrix and druzy, with campsites and cabins. Open roughly mid-April to mid-October.
Fort Plain
Montgomery County- A known Herkimer locality producing sharp, bright crystals. Our Fort Plain pieces are in the shop below.
Fonda
Montgomery County- Herkimer Mountain Diamond Mine: a fee dig at the eastern end of the district.
- HerkimerHistory.com’s research includes samples from the Fonda region.
Plan a dig trip
What to bring
- Safety glasses. Dolomite chips fly when you split rock.
- Heavy gloves and sturdy closed-toe boots
- A crack hammer or small sledge, plus a chisel or pry bar
- A bucket, a small screen or sifter, and a spray bottle to rinse finds
- Egg cartons, tissue, or zip bags so crystals don’t knock together
- Water, sun protection, and a kneeling pad
Three ways to prospect
Scavenging
Search the loose rubble and quarry floor for crystals already weathered out. It’s the easiest and safest method, best the day after a rain when washed crystals flash in the sun. Ideal for kids.
Find and break
Pick up promising dolomite boulders, especially ones with small holes, sparkle, or black carbon, and split them with a hammer to check for pockets inside.
Cavity hunting
Work the rock face with sledges and wedges to open larger pockets. It’s the hardest work but the most productive: one documented cavity held over a hundred crystals.
Tips from the field
- Look for rust-stained or sparkly seams and black carbon in the dolomite. Pockets often follow them.
- Open pockets slowly. The best crystals sit loose inside and break easily under a careless blow.
- Write the mine and date on every bag. A labeled find is worth more.
- Know the law: collecting on New York government land is illegal, and collecting on private land always requires permission. Stick to fee sites or get written landowner permission.
Make a day of it
- Erie Canal Lock 17, Little Falls. Opened in 1916, it lifts boats about 40 feet. When it opened it was the highest lift lock in the world, and it’s still the tallest in the New York canal system.
- Herkimer Home State Historic Site. The home of General Nicholas Herkimer, the county’s namesake, near Little Falls.
- Ilion Gorge. Another Mohawk Valley mineral stop. Read travertine at Ilion Gorge.
- Howe Caverns. About an hour southeast, a limestone cave with an underground boat ride. See how caves are made.
Caring for, displaying, and buying Herkimers
Cleaning
Rinse with water and a soft toothbrush. Mud and dolomite dust come right off. Skip harsh acids on matrix pieces, since dolomite is a carbonate and will etch. See cleaning and storage.
Heat and ultrasonics
Keep enhydros and heavily included crystals away from heat and ultrasonic cleaners. Trapped fluid expands, and internal fractures can spread.
Storage
At 7, Herkimers scratch each other and the sharp points chip. Store them separately in padded boxes or egg cartons, never loose in a bag.
Display
Side light or a small LED under a clear crystal shows off its brilliance. Smoky and black pieces are safest out of long, direct sun.
What drives price
Clarity, size, sharp undamaged points, rare types (skeletal, black, enhydro), matrix, and a confirmed NY locality. More in what makes a specimen valuable.
Photographing
Use a dark background and angled light to catch the faces. Tips in how to photograph a specimen.
Herkimer glossary
- Vug / pocket
- An open cavity in the rock where crystals grew.
- Dolostone
- Rock made mostly of the mineral dolomite. The Little Falls Dolostone hosts every Herkimer.
- Termination
- The pointed end of a crystal. Herkimers are double-terminated.
- Prism
- The six-sided middle section between the two points.
- Matrix
- The host rock a crystal is attached to.
- Floater
- A crystal that grew loose in a pocket, not attached to rock.
- Druzy
- A sparkling crust of tiny crystals coating a surface.
- Enhydro
- A crystal with trapped fluid, sometimes with a moving bubble.
- Anthraxolite / pyrobitumen
- The black, coal-like hydrocarbon found inside and around Herkimers.
- Skeletal
- A crystal whose edges grew faster than its faces, leaving stepped or hollow faces.
- Phantom
- A ghost outline of an earlier crystal inside a larger one. See phantom quartz.
- Fee dig
- A mine that charges admission and lets visitors keep what they find.
Herkimer diamonds in the shop
Real Mohawk Valley material, each labeled with its locality, including a cluster collected at Herkimer Mountain in 2023 and crystals from Fort Plain.
Keep reading
Deep dives from the Crystal Harvest blog.
- The real story behind Herkimer diamonds
- The Mohawk Valley rock layer behind Herkimers
- Why some quartz has a point on both ends
- Smoky quartz: color built by radiation
- Crystal habit: why no two crystals match
- Nucleation: one giant crystal or a thousand small ones
- Inclusions: minerals trapped inside minerals
- Ghost bands, glowing rocks, and black Herkimers
- Rockhounding the Northeast
- What “on matrix” actually means
- Specimen repair and what should be disclosed
- Where crystals come from: sourcing and ethics
- The Mohs scale explained
- The complete quartz guide
- All crystal guides
Frequently asked questions
Are Herkimer diamonds real diamonds?
No, they are quartz. A quick way to tell them apart from a real diamond: Herkimers come out of the ground already faceted with six-sided symmetry, while rough diamonds usually look like rounded, greasy-looking octahedra until they are cut. A diamond is also far harder (10 vs. 7).
How much are Herkimer diamonds worth?
It depends on clarity, size, damage, type, and locality. Small clear points sell for a few dollars, while large, flawless, black, skeletal, or enhydro crystals and fine matrix pieces can sell for far more.
Can I keep what I find at a mine?
Yes. That is the point of a fee dig: you pay admission and keep your finds. Each mine sets its own rules on tools and areas, so check before you dig.
When is the best time to dig?
Most mines open from spring to mid-fall. Many diggers like the day after a rain, when washed crystals flash in the rubble, and cooler spring and fall days for heavy rock work.
Is Herkimer digging good for kids?
Yes, searching loose rubble is very family-friendly. Everyone near rock splitting should wear safety glasses.
Can Herkimer diamonds be used in jewelry?
Yes. They are usually set whole, in wire wraps or prong settings, to keep their natural faces. At hardness 7 they hold up well to wear. Faceting them is rare because they are already brilliant.
Are Herkimer diamonds found outside New York?
Not true Herkimers. Double-terminated quartz grows in other places, including Pakistan, and is sometimes sold as “Herkimer.” The name properly belongs to the Mohawk Valley crystals.
Where are Herkimer diamonds found in New York?
In the Mohawk Valley of central New York, mainly in Herkimer, Montgomery, and Fulton counties. The classic digging areas are around Middleville, Herkimer, Little Falls, St. Johnsville, and Fort Plain, where the crystals grow in cavities in a roughly 500-million-year-old dolostone. Several pay-to-dig mines are open to the public in season.
How hard is it to find a Herkimer diamond?
Small ones are surprisingly easy to find at the fee-dig mines, especially after a rain washes the tailings clean, and most first-time visitors go home with something. Large, water-clear, perfectly double-terminated crystals are a different story: they take patience, a hammer and chisel, and usually breaking into fresh rock to find an intact pocket.
How much is a Herkimer diamond worth per gram?
There is no single per-gram price. Value depends far more on clarity, sharpness of the terminations, size, damage, and special features (inclusions, golden or smoky color, clusters on matrix) than on weight. A gram of small, chipped points can be worth very little, while one gram of a flawless, gemmy crystal can be worth many times more. The “What drives price” section above breaks this down.
Why are Herkimer diamonds worth less than real diamonds?
Because they are quartz, one of the most abundant minerals on Earth, not carbon diamond. They are softer (7 vs. 10 on the Mohs scale) and not rare as a mineral. Their value comes from their natural faceting, clarity, and famous locality, which is why collectors pay well for top crystals even though they will never price like diamond.
Where can I sell Herkimer diamonds?
Options include local rock shops, mineral shows, rock and mineral clubs, and online marketplaces. Clean, undamaged crystals with a documented locality (the mine or town where they were dug) sell best. Photograph each crystal clearly with a scale and list its size and any damage honestly.
What are Herkimer diamonds good for?
Mostly collecting, display, and jewelry: their natural brilliance makes them popular in pendants and earrings without any cutting. They are also widely used in crystal-healing practices, though there is no scientific evidence for those effects. Browse our Herkimer diamond specimens.
Sources and further reading
- HerkimerHistory.com, the Herkimer Diamond Mining District research project by Dr. W. David Hoisington: formation steps, the Oil and Seed Crystal theory, and FAQs on clarity, smoky color, and mine differences.
- Wikipedia: Herkimer diamond: host rock age, Carboniferous crystal growth, late-1700s discovery, inclusion types, alternate names.
- Wikipedia: Little Falls Formation: Cambrian dolomite, stromatolites, host of Herkimer diamonds.
- Mindat: Ace of Diamonds Mine: location and mineral list, including enhydro quartz and pyrobitumen.
- Mine websites for locations and seasons: Herkimer Diamond Mines, Ace of Diamonds, Crystal Grove, Diamond Mountain Mining, Herkimer Mountain.
- Wikipedia: Herkimer County, New York: county formed in 1791 and named for General Nicholas Herkimer (Battle of Oriskany, 1777).
- New York Almanack: Little Falls’ Lock 17: opened in 1916, world’s highest lift at the time.
- Frank Festa, “Herkimer Diamonds I – The Info” (Mindat): early records (Dewey 1819, Hadley 1823, Dana 1837, Beck 1842), A. B. Crim’s exposition awards, Lake George “diamonds,” and notes on the Native American connection.
- University of Waterloo, Wat On Earth: fluid-inclusion growth temperature (~51 °C), depth (~1 km), and healed fractures in ~75% of crystals, citing Ulrich (1989, Rocks and Minerals) and Jensen (1978).
- Geology.com: Herkimer Diamonds: physical properties, mineral inclusions, the three prospecting methods, and New York collecting law.
- NY Senate: state mineral bill S.5866 (2015) and List of New York state symbols: garnet is the state gem (1969), and Herkimer diamond is not an official symbol.
- Wikipedia: Mohawk people: Kanienʼkehá꞉ka, “People of the Flint.”
- Fluorescent Mineral Society: petroleum-included quartz, Balochistan, Pakistan: blue fluorescence under longwave and shortwave UV.
- Teinturier & Pironon (2004), “Experimental growth of quartz in petroleum environment. Part I”, Geochimica et Cosmochimica Acta 68(11): quartz growth and inclusion trapping at high oil saturation, up to 250 °C.
- Hearn & Sutter (1985), “Authigenic potassium feldspar in Cambrian carbonates: Evidence of Alleghanian brine migration”, Science: Late Pennsylvanian to Early Permian basin-wide brine flow in the Appalachians.
- NYSGA 1992 field guide, “The Little Falls Dolostone (Late Cambrian): Stratigraphy and Mineralogy” (PDF): ~50 °C growth, up to ~7 km burial, mineral list, and summaries of Roedder (1979), Bennett & Siegel (1987), Chamberlain (1988), and Ulrich (1989).
- HerkimerHistory.com: Hydrocarbon and Quartz and Hydrocarbons: nine hydrocarbon occurrence patterns, paleokarst evidence, quartz spheres in hydrocarbon cavities.
- HerkimerHistory.com: Scientific information: 200–250 °C argument, Little Falls fault displacement, Leach (2002), Kingston University growth experiments.
- HerkimerHistory.com: Hopper and Skeletal: edge-versus-face growth and supersaturation.
- Kapchai (2018), “Characteristic inclusions of Herkimer quartz and Pakimer quartz” (PDF), Université de Nantes gemmology dissertation: FTIR, Raman, and UV comparison.
- Rock & Gem: Crystal Head Vodka and its Herkimer diamond filter.
Mine seasons, hours, and fees change. Always confirm with the mine before visiting.