Geology of New York

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Herkimer Diamonds

Found in Herkimer County, New York, Herkimer Diamonds are double-terminated quartz crystals. These crystals possess double termination points and 18 total faces. These crystals were discovered in the late 18th century while mining for dolomite. While double pointed quartz can be found in many places, only those mined in Herkimer County can be called Herkimer Diamonds.

Garnet (Almandine)

Streak: white

Hardness: 7 – 7.5

Chemical Formula: Fe3Al2(SiO4)3

Garnets are a group of silicate minerals. Almandine is the most common of the garnet group and always features a red color.

Crystals of almandine often have well-developed faces and complex crystalline structures. Due to its color, almandine garnets are frequently cut and used as gemstones, but coarse varieties are often crushed for use as an abrasive.

Photo: Almandine by Rock Currier is licensed under the Creative Commons Attribution 3.0 Unported license.

sample of smoky quartz


Hardness: 7

Streak: White

Chemical Formula: SiO2

Quartz is one of the most common minerals found in the Earth’s crust. While it is usually colorless and transparent, quartz can also be found in a wide variety of colors and a range of opacity. These varieties generally have their own name such as rose quartz, amethyst, smoky quartz, and citrine.

Quartz can also be found in cryptocrystalline varieties, or quartz that is made up of microscopic crystals. These varieties include chalcedony, agate, and jasper.


Streak: golden-yellow

Hardness: 2.5 – 3

Chemical Formula: Au

Gold generally occurs in tree-like growths or grains. Because of it’s inert state, gold resists tarnish and is generally found in a relatively pure form.

Almost all of the gold recovered from the earth comes from placer deposits, weathered particles concentrated in river gravel. This relatively rare mineral has been used since antiquity in many facets of human life from coinage to art and beyond.

Today, 10% of the gold produced finds its way into industry with much of it being used to produce electronic components.

Photo: Gold by Robert M. Lavinsky is licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license.

sample of pyrite


Streak: Greenish-Black

Hardness: 6 – 6.5

Chemical Formula: FeS₂

Pyrite is the most abundant sulfide mineral. It’s pale brass-yellow color is where pyrite gets its nickname “Fool’s Gold” as it was commonly mistaken for gold by novice prospectors.

The name pyrite is derived from the Greek phrase pyrites lithos, “stone or mineral which strikes fire,” due to the fact that pyrite emits sparks when struck by iron.

Pyrite is well known for it’s cuboid crystal habit, but it can also be found in many other forms. Pyrite can form dodecahedral, or twelve sided, forms known as pyritohedra.

Fool’s gold can be differentiated from real gold by its hardness, brittleness, and crystal form. Pyrite’s streak also is a defining characteristic as it is generally greenish black to brownish black whereas gold tested on a streak plate will leave a yellow streak.

sample of celestine


Streak: White

Hardness: 3 – 3.5

Chemical Formula: SrSO4

Celestine or Celestite is a mineral consisting of stronitum sulfate. This mineral is known for it’s light blue color, although it can be found in other color variations. Celestine can be found in geodes and is most often found in crystal form, but also in compact and fibrous forms.


Streak: Black

Hardness: 5.5 – 6

Chemical Formula: Fe3O4

Magnetite can be found in the precambrian rocks of the Adirondack and Highlands areas of New York and New Jersey. Magnetite is an iron oxide mineral that crystallizes to in the form of masses, octahedral, or dodecahedral crystals. Magnetite in New York can also be found in cube shapes.

Photo: Magnetite by Robert M Lavinsky is licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license.


Streak: White

Hardness: 3

Chemical Formula: CaCO₃

Calcite is found commonly in ore deposits, as a cementing medium in sandstone, or in small quantities in igneous rocks.

These Calcite crystals come in a variety of sizes. Calcite can be microscopic or grow to several feet in length. It’s quite common to see excellent examples of calcite in “dogtooth” shaped crystals. These crystals have a pyramid shape. Calcite does not vary much in color. It is generally white or a pale amber.

Photo: Calcite, Dolomite by Robert M. Lavinsky is licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license.

Large example of pink dolomite with three quartz crystals growing from it

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Author: Celeste