3a. The Evils that beset mineral collections: Temperature changes

In the last installment, I discussed temperature effects, but not temperature change effects.

The largest effect happens in situations where a collection is kept in places that can get below the freezing temperature of water. There is an effect called freeze-thaw disaggregation, which is seen in nature at rock outcrops: water seeps into the rocks and expands as it freezes, prying the rock apart. Minerals with fluid inclusions, or ones that are inadvertently wetted down (does your basement flood?) might suffer from such effects.

The other extreme is rare as an environment, but can occur to specimens with fluid inclusions when viewed through a microscope with hot lights, or while being photographed with hot lights. Some fluid inclusions contain gas bubbles (e.g., carbon dioxide bubbles), and these expand as a specimen is heated. In one anecdotal case, a gemstone exploded when held in someone's mouth.

Temperature cycling can also cause a mineral specimen to disaggregate. Each mineral has its own thermal expansion coefficient, which measures how much it expands as it gets hotter and contracts as it gets cooler. Anisotropic minerals (corundum is a good example) have different thermal expansion coefficients in different directions, and can even contract in some directions while being heated.
A matrix mineral specimen is an aggregation of different grains, often with varying orientation. The grains will typically push against each other as temperature climbs, and pull apart as temperature falls. This might lead to delicate specimens falling apart.

3. The Evils that beset mineral collections: Temperature and Temperature changes

Is global warming a threat to your mineral collection? Maybe.

First, let's talk mineral stability. Many mineral species are described that are not stable at room temperature, pressure, and humidity. However, most are stable in the environments in which they form (some are formed metastably, which won't be discussed more in this blog entry).

To form, minerals need a supply of nutrients (elements), and the appropriate pressure and temperature ranges. The conditions needed for mineral stability also include the relative amount of water available, relative acidity, and oxidation state. Minerals that contain other elements that may be in the gas or fluid phase, such as sulfur, selenium, and fluorine, may have additional requirements for stability.

Now look at minerals that are outside their stability range. Will these immediately decompose? Not necessarily. If the amount of energy needed to start the change or decomposition is high, the mineral may stay in the same state despite adverse conditions. This is called a metastable condition, and the best example is diamond.

However, many minerals do break down, and the conditions on earth that form minerals may not be represented in your collection. The most obvious low-temperature example is ice; another is antarcticite. Neither of these are stable at 20-25 C.

The opposite case is for high-temperature minerals whose crystal structures spontaneously distort at lower temperatures. Probably all so-called specimens of "beta quartz" are now alpha quartz, unless there is a mineral collection that keeps specimens above 550 C.

2. The evils that beset mineral collections: Space

Space, or lack of it, is often a problem for compulsive collectors like me. As zen comedian Steven Wright said, "You can't have everything. Where would you put it?"

Here are some typical space concerns:

Display space: How many of your minerals can be displayed at once? Would you like to display more, and if so, do you rotate the collection so that other specimens are sometimes on display?

What happens when you get new display pieces? Often, the existing display is rearranged to make space for the new specimens. Eventually, display clutter becomes a problem.

Can you see all the specimens on display from one position, or do you have to contort yourself to see what's on a lower shelf, or the items in the corners? If the latter, your display spaces may be too crowded.

Do no specimens touch? Is it clear which label belongs to each specimen? Is every label readable without moving any specimens? If so, you may have enough display space for the specimens you are showing.

Storage space:
Is it archival? Is it secure against rodents, insects, and other pests? Is it secure against theft, weather, and other hazards? These are all reasons that a garage may not be the best place to store some or all of your specimens. Weight and heat may preclude attic storage; water problems may preclude basement storage. You'll have to judge whether any of these will work for you.

For important specimens (or jewelry), you may wish to invest in a box in a bank vault. There are rumors of opals crazing in bank vaults due to lack of humidity, so think twice about storing opals there. You might also wish to save a copy of your mineral records in a remote site such as a bank vault.

Is it accessible? If you need to get access to a particular specimen in storage, it helps to know exactly where it is, and what you need to move to get access to it. It's easy to bury boxes under other boxes, so it's important that every box be labeled on all sides. "This end up" is another important message where needed.

Gemstone storage: For those of you with loose fashioned gemstones, how do you store them? Some people use individual pill-case type containers, some use small plastic bags, and some use stone papers. (Larger specimens or suites are often stored in their own lined cases or Riker Mounts.) Regardless of the storage method, gemstones should not touch each other; even diamonds get "paper wear" from other diamonds in the same stone paper.