MARVELOUS MICROMOUNTS
Magnifying Minerals for a Perfect View
Few mineral deposits are as well known as Franklin, N.J. It has produced well over 200 different mineral species and is undoubtedly one of the most visited by scientists and amateur collectors than any other locality. Its location in northern New Jersey puts it in the densely populated northeast, only an hour’s drive from New York City and in an area where there’s a high concentration of schools of higher learning and museums.
I have spent hundreds of hours collecting in the Franklin area while attending shows and visiting friends. I’ve even written a couple of books and several articles about the area, but have never collected its micro-minerals. Yet, I certainly enjoy looking at them and learning about them.
For convenience, I will refer to micro-minerals as micros, the most commonly used term for them, in this article. The photos of micro mount minerals throughout this article are those of noted micro-specialist Russ De Roo.
The study of minerals under magnification has been going on since the microscope’s invention just before 1600. The microscope played a vital role in studying minerals and discovering new species. Both scientists and amateur collectors have added immensely to mineral species’ lexicon by studying specimens using microscopes. The popularity of micro collecting has long been of significant interest within our hobby. Conferences, symposia, exhibitions, and club field trips have all featured the micro-mineral hobby.
PRIZED PERFECTION
If the study of micro minerals has a by-word, it is “perfection.” Normal-sized specimens are seldom in perfect crystal form for several reasons. To develop perfectly, they have to have space, a steady supply of molecules from the solution or gas from which they are forming. The crystal growth environment, including temperature and pressure and even time, has to remain steady during crystal growth. If any of these conditions vary too much, the crystal is not textbook complete and perfect.
On the other hand, microcrystals are more apt to grow in a stable environment, so perfection is higher. Thus, by studying microcrystals, a collector has a much better opportunity to see perfectly formed crystals. Plus, the study of crystallography is far more gratifying.
When I was teaching science, including earth science, I was lucky to have easy to use microscopes for my students. We would make a super-saturated solution of a soluble mineral, and while the solution was hot, the students could put a few drops on a glass slide and observe what occurred as cooling took place. This experiment gave students a chance to see crystals grow.
FRANKLIN STERLING HILL: MICROMOUNT HAVEN
No locality has generated more interest within New Jersey and yielded more new mineral species than the FranklinSterling Hill companion localities. As of 2017, over forty new species have been found in these two deposits, and more continue to come to light. No wonder micro collecting is a major part of the area’s mineral hobby. Years ago, when I was on the board of the Arizona-Sonora Desert Museum, I was contacted by a good friend from New Jersey, Russ DeRoo, a rockhound who loved micro-minerals. He had accumulated a series of slides of Franklin and Sterling Hill micro-minerals. The Museum had a tremendous micro mineral collection, and these Franklin area slides would fit right in, and I gladly accepted them for the Museum.
One big problem with photographing micros is
the focus. The depth of field in a microscope is very shallow. When viewing a specimen, the collector must continuously adjust the focus to compensate for the field’s depth. Using today’s digital equipment, much better results are possible. All the photos with this article were photographed with a film camera.
Examination of micros is also one tool used to try and answer some age-old geological questions. One such question involves the origins of the zinc deposits at Franklin and Sterling Hill, a complex puzzle. We do know the deposits were initially formed with limestone and later heavily metamorphosed several times over. This process occurred in the Precambrian, and later the ore bodies were invaded by pegmatite solutions. All of this happened while these formations were buried deep in the earth. The latest investigations have shown that volcanism was also involved. Given our recent investigations of hydrothermal vents along ocean crustal boundaries, I believe that these might result from such deposition.
One of the aspects that stumped scientists is the deposit’s three major mineral species franklinite, willemite, and zincite. Of all the world’s zinc deposits, only these two deposits have those three minerals as major ores. Pegmatite intrusion and repeated metamorphism contributed greatly to their development.
Today collectors revel in the great variety of species found here. Those who enjoy collecting minerals that respond to ultraviolet excitation consider Franklin their Mecca, drawn to it with the latest UV equipment knowing their field collecting will be successful. These deposits are so rich in minerals that fluoresce that New Jersey’s state legislature declared Franklin the “Fluorescent Mineral Capital of the World.”
AGES OF APPEAL
While this area’s popularity in modern times is well recorded, long before Europeans arrived in America, these deposits were known to the local native peoples. The outcrops of the deposits are colorful and a ready source of colorful rock that could be crushed and ground to paint and the like. When Europeans did arrive, it was the Dutch who settled in the area. Again, the visible, colorful ores were immediately investigated, not for zinc but iron. Mining of and smelting of iron began, and the settlement was named for Ben Franklin. Because smelting iron ore needs great heat from powerful furnaces, the town was named Franklin Furnace.
Gradually attempts were made to mine and smelt the abundant zinc deposits, but that proved to be a real problem. No matter what the mining people tried, they could never really get a good product. Something in the zinc ore was causing great difficulties. Finally, they figured out that franklinite was an iron-zinc mineral that simply did not smelt like zinc