Sunstone History

This a partial copy of a Gemological paper published in The Ore Bin, written by N. V. Peterson of the Oregon Department of Geology and
Mineral Industries.

I have included at end, the information to the website, where you can read the entire publication.

This shows that the Oregon Copper Bearing Sunstone deposits has been mined and or known about since early Man.
Not all the information is correct or up to date, but is quit useful and informative.

OREGON “SUNSTONE’S”

N. V. Peterson, Geologist
             Oregon Dept. Of Geology and Mineral Industries

Introduction

Within Oregon there is a small but unusual occurrence of semiprecious gems known as “Sunstone.” The locality is in the Rabbit Basin of southeastern Lake County, and the “Sunstone” occur as phenocrysts (large crystals) of gem-quality feldspar in a basaltic lava flow.

Specific field information about the Sunstone occurrence was gathered by the author during three days late in the summer of 1972. Bob Rogers and George Marshall of Portland, Oregon; Don Sellers of Lakeview, Oregon; Truman Mitchell of Milwaukee, Oregon; and Mrs. T. Mapes of Klamath Falls, Oregon, were very helpful in providing information about local geography and about sunstone mining and ollecting in general. They also furnished specimens for study and photographing.

Definition of Sunstones

“Sunstone” is the name given to a certain variety of feldspar that exhibits a brilliant pink to reddish metallic glitter or shimmer. The metallic glitter result from the reflection of light from myriad of minute flat scales of hematite or other mineral impurities. The enclosed scales are so small and thin they appear transparent; however, their reddish color can be seen plainly by examining a thin piece of the feldspar with a magnifier. The mineral inclusions are usually arranged parallel to the direction of perfect cleavage in the feldspar crystal, so the glittering reflection is only seen when looking at the cleavage surface. The glitter or shimmer is called “aventurescence;” crystals of feldspars exhibiting aventurescence are called aventurine or more commonly sunstones.

Sunstones in general occur in both orthoclase and plagioclase feldspars. At the Oregon locality, however, the sunstones consist of crystals of calcic labradorite (one type of plagioclase feldspar); the colors range from red to green as well as the coppery aventurescence.

In most gemology references, sunstone is listed with the feldspar group as a semiprecious gemstone. In the early 1800’s, sunstone was considered extremely rare and was very costly, but with subsequent discoveries in Siberia, Norway, and other parts of the world, it has become more avail¬able and less expensive. In the United States sunstone occurs at several locations, a  partial list of which is given in Table 1. Location and Geographic Setting The Oregon locality is a small area of about 7 square miles in the northern part of the Rabbit Basin in Warner Valley, about 25 miles north of Plush (Figure 1). The area is in the northwestern part of the Rabbit Hills NE quadrangle, Oregon (7.5 minute series, U.S. Geo. Survey topographic map, 1966).

The area can be reached from Lakeview by following State Highway 140 north and east for 20 miles, then proceeding north on a paved county road to Plush. From Plush, gravel and dirt roads continue northward to the sunstone area; signs at road junctions give directions. An alternate route reaches the area via the Hogback Road, which leaves U.S. Highway 395 near the Hogback Summit about 50 miles north of Lakeview. About 14 miles east, at a marked junction, a dirt road leads eastward to the sunstone area. Roads beyond Plush are only periodically maintained, so travel to and from the area is only practical from late spring to early fall.

In this part of Lake County, extreme seasonal temperature changes and a very low rainfall limit the vegetation to low-growing sagebrush and clumps of desert grass. There is no drinking water available in Rabbit Basin, the closest available supply being at Plush.

Rabbit Basin, at an elevation of 4,600 feet is on area of low relief (Figure 2). Occasional arcuate beach ridges mark levels of an ancient pluvial lake that once occupied the basin. The highest shoreline encircles Rabbit Basin at an elevation of about 4,780 feet. In the northern part of the basin, a low, broad north-trending ridge known locally as Dudeck Ridge (Figure 3) is formed by the lava flows that contain the sunstones.

History of the Oregon Occurrence

It has long been known that sunstones, or aventurine feldspar of appreciable size and goad quality occur in the Warner Valley in lake County, Oregon (Figure 4). Locally the sunstones are referred to as “Plush Diamonds,” and it is reported that the old maps of lake County show the “Sunstone Mine.”

The first collectors of Oregon sunstones may have been the Indians that inhabited or traveled through Warner Valley. A group of small stones (Figure 5), some of which show the aventurine glitter, are displayed with the Indian artifacts in the Jacksonville Museum. These sunstones, which are identical to the Warner Valley specimens, were found at Table Rock near Medford in Jackson County by an early resident. Some of the stones appear to have been flaked, and it is probable that the Indians from the Warner Valley traded them with the Rogue Valley tribes.

The reported occurrence of aventurine labradorite from Modoc County, California, listed in Table 1, was described by Olaf Andersen in 1917 and was based on a study of ” a number of pebbles and 6 cut stones in the collection of the U.S. National Museum.” The properties of the feldspar he describes are almost identical to those of the Oregon labradorite. No recent references to a California occurrence in Modoc County can be found, so it is entirely possible that the material described could have come from lake County, Oregon.

Aitkens (1931) in his discussion of the gem varieties of feldspar, states, “About 1908, a report of a discovery of a new deposit of labradorite in southern Oregon was made by Maynard Bixby of Salt lake City, Utah, who stated that this mineral would yield handsome gem material. This labradorite ranges from colorless to a dark variety, showing fine red, salmon, and green tints. “

Dake (1938), in describing the semiprecious gemstones of Oregon, indicates that “Good specimens of Sunstone suitable for cutting are found in the detrital surface materials at localities in the central part of lake County.” He further reports: “The rough gem is sold by the ounce and good material showing the proper amount of included extraneous material brings a price well worth collecting the gem.” Stewart, Walker, and others (1966) describe in detail the physical properties of the transparent calcic labradorite from lake County. In their study they discuss the petrology and petrography of the feldspar-bearing lava flows, chemical composition, optical properties, unit cell parameters, and thermal expansion characteristics of the feldspar crystals. They do not, however, mention the red or green colors or the aventurescence to which some of the feldspars owe much of their appeal. Numerous other short articles giving brief descriptions of the sunstone and information about the locality have appeared in the popular mineralogical journals, lapidary magazines, and rock hound club journals.

Many rock hounds and gemstone collectors have made annual pilgrim¬ages to the sunstone area to search the surface of the ground for stones or to screen the soil cover for buried stones. In 1970 a group of avid collectors discovered that in some places the sunstone-bearing lavas were decomposed beneath the thin veneer of surface soil. They found that by disintegrating the parent material, larger, better-quality, and more colorful suns tones could be recovered. This led to the staking of several mining claims in the area. Subsequently, at the request of organized gem and mineral groups, the Bureau of Land Management withdrew 4 square miles from mineral entry so that anyone desiring to look for and collect sunstones could hove access to a part of the area. The withdrawal boundary and the approximate location of the original group of mining claims is shown on the geologic map (Plate 1).

Go to this web site for the complete paper and others back to January 1939 http://www.oregongeology.org/sub/quarpub/OrGeo.htm Go down the page to 1972 and click on n 12

Oregon Geology (formerly The Ore Bin) is designed to reach a wide spectrum of readers in the geoscience community who are interested in all aspects of the geology of Oregon and its applications. Informative papers and notes, particularly research results, are welcome, as are letters or notes in response to materials published in the journal. Conclusions and opinions presented in articles are those of the authors and are not necessarily endorsed by the Oregon Department of Geology and Mineral Industries.

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