Rockhounding in South Dakota – What Rocks You Can Find and Where

Rose Quartz

Streak: White

Hardness: 7

Chemical Formula: SiO₂

South Dakota is known for Rose Quartz, a pink variety of quartz that may feature diasterism, or star-like shape of light when illuminated from behind when shaped and polished.

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.

Photo: Mineral Cuarzo Rosa by Luis Miguel Bugallo Sánchez is licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license.

Agate

Streak: White

Hardness: 7

Chemical Formula: SiO₂

Agate is a common form of chalcedony, a microcrystalline form of quartz. It’s banded, colorful appearance has lead to its widespread use throughout human history.

Most varieties of agate are named for its visual appearance, such as fire agate which has inclusions of red or brown hematite. Agate can also vary in its banding appearance, some agates have a dendritic habit or lace-like patterns with eyes, swirls, and other patterns.

Because this mineral is a form of quartz, it’s hardness lends itself to uses not commonly associated with such visually appealing minerals. Agate has been used to create precision pendulums, mortars and pestles, and fine knife-bearing edges for laboratory balances.

Photo: Agate by James St. John is licensed under the Creative Commons Attribution 2.0 Generic license.

Petrified Wood

Petrified wood forms when plant debris is buried by sediment and then replaced by deposition of mineral material dissolved in groundwater.

Photo: Petrified Wood by Diego Delso, delso.photo, License CC-BY-SA“

Gold

Streak: Golden, Yellow

Hardness: 2.5 – 3

Chemical Formula: Au

Native gold is an element and a mineral. It is highly prized by people because of its attractive color, its rarity, resistance to tarnish, and its many special properties – some of which are unique to gold. No other element has more uses than gold. All of these factors help support a price of gold that is higher than all but a few other metals.

Trace amounts of gold are found almost everywhere, but large deposits are found in only a few locations. Although there are about twenty different gold minerals, all of them are quite rare. Therefore, most gold found in nature is in the form of the native metal.

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