Granite Mountain
In the Arkansas counties of Saline and Pulaski (reaching the Little Rock city limits) is a complex intrusion of medium- to coarse-grained syenite, that crops out in a belt. The part in Saline County is weathered, and there are just traces of old bauxite mining. The intrusion consists of two major units. The older, an altered olivine syenite, is best exposed in Pulaski County in several active quarry operations. The younger, an analcime nepheline syenite, is best exposed in Sabine County, but no active quarries exist in this area. The overall intrusion is batholitic in proportion, but only the higher portions of the intrusion have been exposed by erosion.
It is supposed, that the syenite crystallized in the lower crust due to introduction of alkali elements and volatiles. Partial melting through the introduction of water was followed by near-surface implacement of semi-crystallized mush, with the remaining melt crystallizing as a fine-grained intergranular material. There are several intergrading metasomatic units in the intrusion with unusual xenoliths.
The minerals occur in 3 types of occurrences: in gas cavities near contacts with wall rock, in pegmatites and pegmatite dike rocks, and in xenoliths.
Mineral list: (bold = type locality)
&Suggested Reading:
Barwood,H.L.: Mineralogy of the Granite Mountain Syenite, Pulaski and Saline Counties, Arkansas. Rocks&Minerals, 64(1989), pp.314-322
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