Penn Minerals! - Classic Minerals and More from Pennsylvania

Jay L. Lininger,  Dillsburg, PA

Webmaster's Note:  The following six part article was originally written by the late Jay Lininger for the Central Pennsylvania Rock & Mineral Club and published in ROCK BUSTER NEWS, an award winning newsletter.  Jay Lininger was well known in Pennsylvania mineralogical circles.  He was co-founder and publisher of MATRIX - A Journal of the History of Minerals, now available for purchase at Penn Minerals.


Many of you reading this article have visited or are at least familiar with the location we call Moore's Mill. The location, which has produced some of the finest phosphate minerals found in Pennsylvania, is located about four miles west of the village of Mt. Holly Springs in Cumberland County.  My fascination with the location began in 1962, when as a young collector I struggled to find it for the first time. In "those days" there was no popular field collecting guide such as the Geological Survey Publication G33. Using my treasured and well-worn copy of Samuel Gordon's "Mineralogy of Pennsylvania" (1922), I spent hours hiking out on the northern rim of the South Mountain searching for what turned out to be a small water filled pit that was incidentally, not covered with bags full of collectable minerals. Just what was this, one of a kind mining operation that lay hidden in the woods outside of Mt. Holly?   Over the years, I've been able to fill in some of the pieces.


The South Mountain of the nineteenth century was an area which bustled with activity. The iron mining industry in the Commonwealth was in full production during that era. Coupled with the development of the coal fields to the north and west, the two commodities had propelled Pennsylvania into the industrial giant among the states. The South Mountain had produced its share of successful iron manufacturing operations with several dating back to the earliest days of the American Revolution. Several notable operations included the Pine Grove-Laurel Bank area (Cumberland County), the Mont Alto complex (Franklin County), and the Catoctin operation in northern Maryland. As active prospecting took place in all areas of the South Mountain, a number of large and valuable white clay deposits were located, particularly in the Mt. Holly Springs area. The geological forces which deposited the large residual beds of iron ore, had also deposited large beds of pure white clay. A new industry thus developed at Mt. Holly Springs in the era following the Civil War. The clay was well suited to the manufacture of tile and brick, and was found to be an excellent whitening agent in the manufacture of paper. Sometime during the latter part of the 1880's, (no actual date has been recorded), the deposit of clay near Moore's Mill was located. The clay at this location was as pure as the deposits on the other side of the mountain, but had one peculiar characteristic. It was contaminated by numerous large pods of a hard clay that was later discovered to be pure aluminum phosphate - wavellite. The discovery of this curious deposit in an area known as the Stuart tract, prevented its exploitation as a clay mine for several years.

History doesn't record who recognized the potential that existed in the bed of phosphate nodules, but someone connected the value of the ore with the newly developing industry in the manufacture of safety matches. The flammability of pure phosphorous was known for many years, but had no practical use until the invention of the safety match in 1855. This handy little device consisted of a wooden matchstick with a phosphorous coating on the tip. The phosphorous was covered with an air tight coating which could be removed by striking the match tip on a coarse surface, thus igniting the phosphorous. Up to this point all phosphorous used in safety match manufacture was processed from animal bones or organic rock phosphate deposits. The bone or rock phosphate was crushed, roasted and treated with sulfuric acid to produce the refined product. Now confronted with an available source of high grade ore, a new reduction process would be required.

In 1898 a group of Philadelphia businessmen formed a new venture which they named the American Phosphorus Company. Aware that they would need to develop a new ore reduction process, they hired G.C. Landis, a well known chemist to supervise the effort. The company began construction of a processing plant and moved to acquire the ore deposit. The land which contained the phosphate bearing clay was owned by T.J. Spangler of Mt. Holly Springs. Spangler was convinced that the deposit had great value, and instead of selling the land, devised an arrangement in which he would be superintendent of the mine, and would be paid by a royalty on each ton of ore extracted. He of course would be in a good position to monitor how much ore was extracted.

The mine was opened in 1900, but several non-productive years were spent in prospecting the deposit and the experimentation in reducing the ore. G.C. Landis was familiar with the patents available in phosphorous reduction, and drawing on this knowledge devised a method to smelt the wavellite in a satisfactory manner. The process required the introduction of great heat, and could only be attained by the use of the newly invented electric furnace. By 1905 all aspects of the mining and ore processing were in full operation. The ore was extracted by pick and shovel and hauled down the mountain to the mill which was situated near the bank of the Yellow Breeches Creek. About 400 tons of ore was mined in 1905, but the open pit, now about 30 feet deep, began to experience severe water problems. Later in the year a test shaft was sunk near the open pit. At the 12 foot level, a large clay mass was encountered, which proved to be 40 feet thick. At the base of clay, the miners struck 16 feet of manganese ore.

In spite of the early successes, signs of economic trouble were on the horizon. The processed phosphorous was a dangerous commodity, and some apparent mishandling led to a disastrous fire in the fall of 1905. This was a setback that caused a disruption in the processing of ore, but the company management raised the necessary capital to rebuild the plant. Water continued to plague the mining of ore, and its removal increased the cost of recovery. Several months after the rebuilt processing plant went back into operation, the management of the company recognized that the cost of operation for the electric reduction was greater than the value of the phosphorous it produced. In a desperate move to regain some semblance of profitability, the company owners decided to move the processing plant to York Haven, which was located by the Susquehanna River. In so doing, the company could obtain more cost effective (river turbine) electricity for running the furnace. The move was successfully completed by the early part of 1906.

During the summer of 1906 the mine was visited and described by George W. Stose, the eminent Appalachian geologist who was working for the U.S. Geological Survey. During his visit the mine was filled with water, but the miners were building a drainage channel to carry excess water downhill. This engineering solution helped keep the mine in workable condition for several more years. In spite of attaining maximum efficiency, the American Phosphorous Company was unable to earn the profit it needed to survive and was closed by the end of the decade. Once again, a well conceived American enterprise failed because technological problems could not be overcome.

The mine had been closed for a number of years when it was visited by Pennsylvania's pre-eminent mineralogist Samuel G. Gordon in 1919. Although existence of the location was mentioned in a publication by mineralogist John Eyerman (1911), Gordon was likely to have been the first mineralogist of note to visit the occurrence. The Cumberland County of 1919 was a sparsely populated agricultural county, and thus Gordon, when preparing his field notes, placed the mine near the closest location of note: Moore's Mill. This was a reasonable assumption for the time, because the numerous grain grinding mills along the Yellow Breeches Creek were important landmarks in the community. When Gordon published his findings in the Proceedings of the Academy of Natural Science in Philadelphia later that year, he forever enshrined the name of Moore's Mill in the mineralogical literature.

Gordon later analyzed the abundance of species collected on that field trip and confirmed the presence of five distinct phosphates: wavellite, cacoxenite, beraunite, variscite and strengite. The variscite and strengite were new species to Pennsylvania.


Little attention was paid to the location until 1965 when Davis Lapham and Allen Geyer published the first of the three popular editions of G33, "Mineral Collecting in Pennsylvania." Soon mineral collectors were able to easily locate the obscure location. As a young collector, I was fortunate in being able to collect each of the species described by Gordon, even though several were rare. One of them was a blue-green massive mineral which was found intergrown with wavellite in the hard nodules. I presumed this mineral to be variscite. And why not? Wasn't variscite a bluish-green mineral? More experienced collectors were auspicious however, including early CPR&M club member Dorothy Herman. Dottie was an astute and knowledgeable field collector, and the massive blue mineral made her curious enough to take it to state mineralogist Davis Lapham for investigation. His subsequent analysis determined the species to be turquoise. Dottie Herman's effort produced a species new to the Pennsylvania list in 1965. The true variscite at Moore's Mill occurred in clear to pale violet radial crystal clusters and botryoidal masses.

Increased collecting of the area was conducted by a new generation of Pennsylvania collectors in the 1970s. The group, unofficially headed by Martin Anne of Wrightsville, decided to excavate in an area north of the pit which they presumed to be the ore loading zone. Their efforts were rewarded with the discovery of numerous large superb specimens of cacoxenite and beraunite. A photograph of one of these specimens was featured on the cover of the special Pennsylvania issue of ROCKS AND MINERALS magazine (May-June 1978).

This story provided a brief overview of the hundred year history of Pennsylvania's most unusual phosphate occurrence. Do other undiscovered phosphates still exist at Moore's Mill? It is likely that they do, and perhaps another chapter in the story of this unique Central Pennsylvania mineral location is waiting to be written in the future.

 Stay Tuned for Part Two!  "The Copper District of Adam's County"