Lab 2: Mineral Properties and Non-Silicate Minerals
|Recommended additional work||Yes – review concepts from Labs 1 and 2 in preparation for Test 1|
|Required materials||Mineral ID kit, Mineral Kits 1 and 2, pencil|
After reading this chapter, completing the exercises within it, and answering the questions at the end, you should be able to:
- Describe mineral lattices and explain how they influence mineral properties.
- Categorize minerals into groups based on their compositions.
- Describe some of the important techniques for identifying minerals.
- Identify and describe the physical properties of a range of non-silicate minerals in hand sample.
- Discuss the economic uses of non-silicate minerals.
Minerals are all around us: the graphite in your pencil, the salt on your table, the plaster on your walls, and the trace amounts of gold in your computer. Minerals can be found in a wide variety of consumer products including paper, medicine, processed foods, cosmetics, electronic devices, and many more. And of course, everything made of metal is also derived from minerals.
As defined in the introductory chapter, a mineral is a naturally occurring combination of specific elements arranged in a particular repeating three-dimensional structure (Figure I4).
“Naturally occurring” implies that minerals are not artificially made. Many minerals (e.g., diamond) can be made in laboratories, but if they can also occur naturally, they still qualify as minerals. “Specific elements” means that most minerals have a specific chemical formula or composition. The mineral pyrite, for example, is FeS2 (two atoms of sulfur for each atom of iron), and any significant departure from that would make it a different mineral. But many minerals can have variable compositions within a specific range. The mineral olivine, for example, can range all the way from Fe2SiO4 to FeMgSiO4 to Mg2SiO4. Intervening compositions are written as (Fe,Mg)2SiO4 meaning that Fe and Mg can be present in any proportion, and that there are two of them for each Si present. This type of substitution is known as .
Most important of all, a mineral has a specific “repeating three-dimensional structure” or “lattice,” which is the way in which the atoms are arranged. We’ve already seen in Figure I4 of the introductory chapter how sodium and chlorine atoms in halite alternate in a regular pattern. Halite happens to have the simplest mineral lattice, most other minerals have more complex lattices. Some substances that we think must be minerals are not because they lack that repeating 3-dimensional structure of atoms. Volcanic glass is an example, as is pearl or opal.
The substitution of one element for another in a mineral (e.g., iron can be substituted for magnesium in the mineral olivine).