Monday, June 27, 2011

The evils that beset mineral collections: 13. Sulfur, Pyrite, and Other Minerals

Minerals that damage other minerals?  Read on, oh Viewer...

A standard way to display minerals is in Dana Order: by anion group starting with native elements, sulfides and sulfosalts, and simple oxides; and ending with framework silicates. A major problem with this display procedure is that it puts elemental sulfur and elemental silver in proximity.  (Note that alphabetical display order also has this problem, though.)

What's so bad about that? Sulfur has a high vapor pressure, meaning that sulfur releases gas at room temperature and pressure. (It has a pronounced smell.)  In a small enclosed place, concentrated sulfur vapors react with metallic elements and sulfides, such as native silver and native copper, to create surface tarnish layers. This makes the tarnished minerals less attractive and can lead to their decomposition.

Pyrite and marcasite have a different problem.  These minerals decompose in humid conditions, producing sulfuric acid. A microbe is thought to be involved. Some museums store these minerals isolated in evacuated plastic bags to prevent them reacting with their surroundings: dissolving labels, boxes, and so on. Another reason for isolation however is to prevent specimens from contaminating each other, if a microbe is involved.

Finally, some radioactive minerals are alpha emitters, and as such can create radiation damage in other minerals if left in very close proximity (touching) for long periods of time. This process often happens in nature (producing for instance smoky quartz), and could possibly happen in collections left alone for decades; however, I know of no examples of this.

Monday, June 20, 2011

The evils that beset mineral collections: 12. Loans, Trades, and Other Collectors

Surely your fellow collectors can be relied upon to leave your specimens undamaged and in your possession! Well, not always... There were rumors in my youth about an esteemed professor -- now long deceased -- being searched as he left a country, with the search revealing several important specimens from the country's national collection. And some people are accident-prone. Most of your fellow collectors are undoubtedly honorable people, but if you don't want to suspect your fellows, and wish to prevent mishaps, there are some things you can do to protect your collection.

When showing your collection to a group, only show it in closed cases. You can open a case to hold up (or pass around) a specific piece, but don't leave people with unsupervised access; they might knock something over.

If you are showing your collection to an esteemed guest, let him or her ramble with you at their elbow to explain, describe, and tell stories about your wonderful specimens.

Trades have two sets of hazards. You may get the worst part of the bargain, but that is an inevitable part of a collector's education. Learn from your mistakes.

The second hazard lies in the exchange circumstances. Pack any specimens to be mailed securely. Be prepared to deal with the circumstance that your trade partner's specimens may get damaged, and have an agreement in place as to how the two of you will deal with damages or mail losses. You may want to send things using a secure form of transportation, such as registered insured US Mail.

When you loan pieces, the loan is usually for a display or to a museum. A loan should have a clear description of who is responsible for transporting the piece, and a clear notion of the duration of the loan. Many museums have special loan paperwork. Also think about security and insurance for your loans. If something happens to the destination site -- a theft, a fire, etc. -- you should be able to demonstrate that the item in question belonged to you.

Sometimes items are sold or traded on approval; again, have an agreement in place in writing before you send out an item.

The purpose of written agreements is to make a trade, loan, or other deal run smoothly when unexpected events occur.

Monday, June 6, 2011

GIA Symposium Poster: for Gem Dealers who want to sell Mineral Specimens.

Last week I attended the 6th GIA Symposium, which was about research and business of gem materials. I mainly attended the research track, especially colored stone and pearl research. I also was able to attend the field trip to some Pala mines prior to the Symposium.

My poster, intended for gem dealers, explains what mineral collectors are looking for in a specimen. Some gem rough can be sold as mineral specimens, but the proper material must be recognized and marketed appropriately.

The images are from Rock Currier, and are copyrighted by him. These can also be found on the website.

Email me at if you would like a copy of the PDF file.