Sheahan Quarry, Graniteville, Iron County, Missouri, USAi

Regional Level Types
Sheahan Quarry	Quarry
Graniteville	Village
Iron County	County
Missouri	State
USA	Country

Graniteville, Iron County, Missouri, has been for some time the most important granite quarrying center in the state. The Sheahan quarry located just north of Graniteville village is at present the most active one in the district. The quarry product is the distinctive "Missouri red granite” of pre-Cambrian age. The granite, a pegmatite, and replacement veins exposed in the quarry afforded material for a petrographic and chemical study presented in this paper.

Feldspar and quartz make up 96 to 97 per cent of the granite. The feldspar includes two generations of albite, orthoclase and microcline. Both orthoclase and microcline are intergrown with albite, forming several types of perthite. Microcline-albite intergrowths are usually of the type described by Andersen as "vein" perthite. The orthoclase-albite intergrowths are much less regular and are of the “patch” type. A third perthitic development is "poikilitic"; allotriomorphic to hypidiomorphic crystals of albite are included in larger crystals of vein and patch perthite. The earliest feldspar of the granite is an albite near oligoclase which occurs in crystals up to an inch or more in length. Albite also appears to be the last feldspar, a second generation of this mineral occurring in small unaltered grains interstitial to the Larger minerals and sometimes as a “blocky” fringe bordering earlier feldspar (Fig. 1). Other minerals, some of which are secondary products, include apatite, biotite, calcite, chlorite, fluorite, hematite, leucoxene, magnetite, muscovite, pyrite, sericite, and zircon. Apatite is very rare, and only a {ew scattered crystals were noted. Biotite is not common and has been largely altered to "green-biotite" and chlorite. A few grains of zircon with characteristic haloes are found as inclusions in the biotite

Magnetite is of interest because it occurs both as an early and as a late mineral. In the second occurrence it is usually associated with muscovite which replaces feldspar and to a lesser extent quartz. It is possible that the muscovite is deuteric and was derived from an earlier iron-bearing mineral such as biotite by the action of late magmatic juices. Such a reaction might produce mica more closely allied to muscovite at the same time liberating iron which became fixed as magnetite. The muscovite is colorless or has a faint olive-green to colorless absorption. It is probably a closely related if not the same mica which occurs abundantly in the pegmatite and veins.

Although pyrite was not observed in thin sections prepared from chips taken from the material used for chemical analysis, this mineral is present in the granite near joint planes. The chlorite apparently derived from biotite is blue-green in color and is characterized by blue-grey interference colors. 2V is small and negative, and the mineral is probably negative-penninite or delessite.

MINERALOGY:
Most of the pegmatite in the outcrop is composed of feldspar and quartz. Topaz, mica, fluorite, and a few other minerals are present, but of special interest is beryl, a mineral hitherto not described in any Missouri occurrence.

BERYL: Massive beryl is common, but there is a greater tendency for this mineral to develop crystal forms than is true of the topaz. Hexagonal prisms two inches in length were found. The beryl varies from colorless or a faint blue to a fine aquamarine color, but none is of good gem quality.

TOPAZ: The topaz is colorless or light yellow with a vitreous luster. It occurs in coarsely granular aggregates, and crystal faces are rare. Topaz is always in close association with beryl and muscovite, and replacement by these minerals and by albite is so general that the original relationships of the topaz could not be determined. Topaz is considered to be the earliest hydrothermal mineral.