Arkansas Novaculite

Figure 3.14. Manganin stress-wave profiles for Arkansas novaculite at 25 GPa (Grady et al., 1974).

Limestones (Knauth and Epstein, 1976), the maximum 5 0 values of all Precambrian cherts are lower than those of Phanerozoic marine cherts (Figure 2). Representative S Osmow values of Phanerozoic cherts are +35%o for fibrous quartz from Eocene deep-sea chert (Knauth and Epstein, 1976) and + iQ%c to +34%o for Devonian Arkansas novaculite chert precipitated at shallow depth (Jones and Knauth, 1979). In contrast, the maximum 5 0 of chert in Paleoproterozoic iron formation is +2A.Wcc to +24.7%o (Winter and Knauth, 1992 Becker and Clayton, 1976 Perry et al., 1973), and 5 0 values for Archean chert are even lower, - -22%o for 3,400 Myr Onverwacht formation chert (Knauth and Epstein, 1976) and +20%c for metachert in 3,700 Myr Isua iron formation (Perry et al., 1978). 

Jones D. L. and Knauth L. P. (1979) Oxygen isotopic and petrographic evidence relevant to the origin of the Arkansas Novaculite. J. Sedim. Petrol. 49, 581-598. 

Importantly, fracture permeabilities may either reduce or increase, in surprising ways, depending on the paths of stress or chemical potential. We illustrate this behaviour through observations during flow-through tests on samples of varied rock types. These include a fractured porous medium (Berea sandstone), and fractures in both silicic (Arkansas novaculite) [Polak et al., 2003 Yasuhara et al., 2004] and carbonate rocks (Bellefonte Limestone) [Polak et al., 2(X)4]. 

The flow experiment was conducted on a cylindrical core (25 mm diameter x 90 mm length) of low porosity (<1%) Arkansas novaculite containing a single diametral natural fracture. 

Sharp silica sand is used as a filler in resinous cement mortars and to provide an abrasive surface in polymers. Reactive silica ash, produced by burning rice hulls, and a lamellar filler, novaculite, which is obtained from the novaculite uplift in Arkansas, are also used as silica fillers in polymers. 

Novaculite no- va-kyo- llt [L novacula razor] (1796) n. A very fine-grained type of quartz found in Arkansas, Georgia, Massachusetts, North Carolina, Oklahoma, and Tennessee. A variety known as altered novaculite, typically about 99.5% quartz, is a solid crystalline substance with the basic hardness of quartz but more easily reduced to very fine particles. At their surfaces, these particles have high concentrations of ruptured Si-O bonds that readily combine with water to create surface hydroxides called silanols. Such novaculites are useful as semi-reinforcing filers in silicone rubber, epoxy resins, urethane foams, and PVC. 

Origin Novaculite Uplift—Arkansas, USA Scientific Description A natural microfon of quartz in a bound and free state of subdivision... 

Silica, Microcrystalline - ml-kro- kris-to-lin n Si02 Pigment White 27 (77811). Extender pigment obtained from extensive geologic formations of hard, compact, homogeneous, microcrystalline silica located in the vicinity of Hot Springs, Arkansas. Can be considered as a very finely divided or micro form of quartz in a bound state of subdivision. Excellent dielectric and low abrasive properties. Density, 2.65 g/cm (22.1 lb/ gal) O.A., 20.0 mean particle size, 4.0 pm. Novaculite is a generic name. Syn Novacite. 

---