AGGREGATE

Novaculite is a very durable rock that resists abrasion and is well suited for use as road base, railroad ballast, and rip-rap. Although it works especially well, its use in these applications is avoided. The reason: novaculite is so abrasive on metal that it causes excessive wear on excavating equipment used to mine it, on crushers and classifiers used to process it, and it wears out the beds of trucks that haul it. Novaculite is also not used as a concrete aggregate for the same reasons and because it reacts with cement to produce pop-outs (aggregate grains that separate from the concrete to produce a pit in the pavement surface).

REFRACTORY

Novaculite’s heat-resistant properties make it a good material for making refractory products. It has also been used in glass manufacturing, with some of it being used in Pyrex products. The abrasive properties of novaculite make it useful for manufacturing deburring media, files, and grinding media.

TRIPOLI

The upper portion of the Arkansas Novaculite Formation in some areas has a significant carbonate content. In these areas the novaculite weathers to yield a granular quartz residue with a very high silica content and a very fine grain size. This material is mined and processed into a product known as tripoli. Most of the tripoli used in the United States today is a filler or extender in plastics, rubber, paint, caulking compounds, and other products. Tripoli is added to soaps and scouring powders to serve as an abrasive. It is also used as an abrasive in metal finishing, woodworking, lapidary, and auto painting shops.

RESERVOIR ROCK

Novaculite sometimes serves as a reservoir for oil and natural gas. Several oil and gas fields in the Ouachita overthrust belt of Oklahoma and Texas produce from the Caballos Novaculite. Tripolitic chert zones near the top of the rock unit can have significant porosity, and the highly fractured novaculite is another form of porosity. Areas underlain by fractured novaculite are also preferred drilling sites when drilling for groundwater.

GOLD TESTING

Small blocks of black novaculite are also used in the “acid test” for determining the gold content of jewelry. In this, the jeweler rubs the suspected gold item across a fine-grained block of black novaculite to produce a tiny streak of metal. A drop of aqua regia (a mixture of hydrochloric acid and nitric acid) of known concentration is placed on the streak. If the streak disappears, it was dissolved by the aqua regia. Aqua regia solutions of different concentration will dissolve different karat weights of gold. Standard aqua regia solutions have been developed to identify gold of 10k, 12k, 14k, 18k, 20k, and 22k purity.

Physical Properties of Novaculite
Color	Usually ranges from white, through gray, to black. Other colors occur when the stone has impurities – brown, red, pink, bluish.
Streak	Colorless (harder than the streak plate)
Luster	Usually dull to earthy when porous. Specimens with very little porosity can have a waxy luster.
Diaphaneity	Translucent on thin edges to opaque.
Cleavage	None – typically breaks with a conchoidal fracture.
Mohs Hardness	7
Specific Gravity	2.5 – 2.7
Distinguishing Characteristics	Conchoidal fracture, glassy luster, hardness.
Chemical Composition	Silicon dioxide (SiO2). Some specimens contain up to 99% silicon dioxide. Some specimens have a high carbonate content of up to 30%.
Uses	Used to make cutting tools, sharpening stones, streak plates, and tripoli. Reservoir rock.