Novaculite is a unique metamorphic rock native to only the Ouachita Mountains of Arkansas and Oklahoma. It is also known as Arkansas Novaculite, and the people of Arkansas have used it for centuries.

American Indians in these regions used Novaculite as a primary raw material for making sharp-edged tools. It was obtained from outcrops on mountain ridges. The debris left behind by mining created the biggest archeological sites in Arkansas.

It is a hard, fine-grained, dense rock with high silica content. The word Novaculite is derived from the Latin word novacula (sharp knife, dagger, razor).

Chemical Composition

Some specimens may have up to 99% silicon dioxide, and some have a high carbonate content of up to 30%.

Physical Properties

• Color: Usually white, gray, or black. Due to impurities, some specimens have brown, red, blue, and pink colors.
• Streak: Colorless
• Luster: Dull to earthy
• Diaphaneity (ability to transmit light): Translucent to opaque
• Cleavage: None
• Mohs Hardness: 7
• Specific Gravity: 5 – 2.7

Novaculite Formation

Single-celled algae and other organisms in marine environments secrete hard shells made of silicon dioxide. When these organisms, also known as diatoms, die, the shells settle at the sea bottom. These shells make up most of the underwater sediment in some areas.

The silicon dioxide in the shells is changed into chalcedony. The rock is known as chert at this point. It is transferred into novaculite as the process continues. The low-grade metamorphism converts the chalcedony into microcrystalline quartz grains. This process of rock transformation is known as diagenesis.

Two major differences identify chert and novaculite. First, chert is made up of chalcedony, while novaculite is mostly microcrystalline quartz grains. Second, chert is a sedimentary rock; novaculite is a chert that has undergone low-level metamorphism and high-level diagenetic changes.

Where is Novaculite Found?

Novaculite isn’t found in many countries. The most notable and biggest reserve is located in the Ouachita Mountains in Arkansas and Oklahoma. It is corrosion-resistant and stands out as a ridge in these mountains. It is also found in the Marathon Uplift and Solitario regions of Texas. Some small reserves are also located in Syria, Japan, Israel, and Lebanon.

Novaculite Uses

• Novaculite is a hard and dense stone. It has been used since prehistoric times by American Indians to make sharp-edged durable tools. Ottoman people also used it to make tools.
• European settlers in Ouachita used novaculite as a sharpening tool for metal and weapons. They were the second people to mine the rock after Native Americans.
• Novaculite is a heat-resistant rock. This makes it an ideal material for refractory materials.
• Novaculite damages metal equipment. Hence it is not used for road base, railroad ballast, and rip-rap.
• Black novaculite is used for acid testing to determine the gold content in jewelry.