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Site content related to keyword: "Sillimanite"

Deal Formation

Td

It is a clayey, calcareous, shelly, glauconitic (10-20 percent) silt. Its colors range from greenish-gray and gray-green to brownish-gray and light gray. It is rich in calcareous and siliceous microfossils. The matrix mineralogy shows a high calcite component, except in the lower part of the formation which is within a calcite dissolution interval. In the lower half of the formation quartz is predominant.

Common Rocks and Minerals of the Delaware Piedmont

The Red Clay Creek has flowed through the rolling hills of northern Delaware for many thousands of years, cutting a deep valley into the old deformed rocks of the Appalachian Piedmont. The Red Clay valley contains many of the common rocks found throughout the Delaware Piedmont.

Setters Formation

Osq

In Delaware, predominantly an impure quartzite and garnet-sillimanite-biotite-microcline schist. Major minerals include microcline, quartz, and biotite with minor plagioclase, and garnet. Muscovite and sillimanite vary with metamorphic grade. Accessory minerals are iron-titanium oxides, zircon, sphene, and apatite. Microcline is an essential constituent of the quartzites and schists and serves to distinguish the Setters rocks from the plagioclase-rich schists and gneisses of the Wissahickon Formation.

Wissahickon Formation

Owf

Interlayered psammitic and pelitic gneiss with amphibolite. Psammitic gneiss is a medium- to fine-grained biotite-plagioclase-quartz gneiss with or without small garnets. Contacts with pelitic gneiss are gradational. Pelitic gneiss is medium- to coarse-grained garnet-sillimanite-biotite-plagioclase-quartz gneiss. Unit has a streaked or flasered appearance owing to the segregation of garnet-sillimanite-biotite stringers that surround lenses of quartz and feldspar. Throughout, layers of fine to medium-grained amphibolite composed of plagioclase and hornblende, several inches to <30 feet thick or as large massive bodies, are in sharp contact with the psammitic and pelitic gneisses. An attempt has been made to show some of the amphibolites mappable at the scale of the map. Granitic pegmatite is ubiquitous and occurs at all scales. Pyroxene bearing quartzite with garnet occurs locally near the contact with the Wilmington Complex. An ultramafic lens composed of cumulus layers of serpentinized peridotite, metapyroxenite, and metagabbro occurs near Hoopes Reservoir. The ultramafic lens may be correlative with the Baltimore Mafic Complex.

Delaware State Mineral - Sillimanite

Sillimanite - Delaware State Mineral

In 1977, the Delaware General Assembly, acting on a proposal by the Delaware Mineralogical Society, established sillimanite as the Delaware State Mineral. This act recognizes the geological and mineralogical significance of the large masses of this mineral found as boulders at Brandywine Springs, an occurrence that was recognized as important in the 6th (1892) edition of Dana's System of Mineralogy. The Brandywine Springs boulders are remarkable for their size and purity. The sillimanite has a fibrous texture reminiscent of wood and could potentially be cut into cabochon gems showing a chatoyant ("cat's eye") effect. Sillimanite is not mined as an ore or raw material in Delaware.

Sillimanite established as Delaware State Mineral

Sillimanite - Delaware's State Mineral
Date: Jan 1977

In 1977, the Delaware General Assembly, acting on a proposal by the Delaware Mineralogical Society, established sillimanite as the Delaware State Mineral.

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Schenck rocks out on railroad geological tours

William S. Schenck of the Delaware Geological Survey prepares students for a rock excursion.

William S. Schenck, a scientist with the Delaware Geological Survey, has been taking students from A.I. duPont High School on Wilmington & Western Railroad tours, observing rock outcrop locations along the way.