Rhyming Peg Mnemonic Device Applied to Learning the Mohs Scale of Hardness, The

Journal of Geoscience Education, Nov 2003 by Rule, Audrey C

ABSTRACT

The rhyming peg mnemonic device, appropriate for learning an ordered set, is used to teach Mohs hardness scale. Students begin by learning the "pegs" - a set of words, each rhyming with a number from one to ten, to which each mineral will be linked. Students then study, interpret, make additional connections with, personalize, and visualize a set of illustrations that associates each mineral with its peg word, number, and attributes. This technique is effective because it is meaningful, helps students organize information, provides many associations, uses the creative thinking skill of visualization of images, and focuses student attention. The following poem contains couplets describing each of the ten mnemonic drawings.

See the sweating, slipping sun,

Rating talc as number one.

Buy a gypsy's gypsum shoe,

Or a scratched-up pair of two.

Trim the cave-rock calcite tree,

Always branching into three.

Shut the bulging fluorite door,

That the toothpaste labels "four."

Fear the crossed-bone killer hive

With an appetite for five!

Orthoclase-tipped music sticks,

Beat a rhythm pounding six.

Seven jars, all cloudy quartz

Hold crystals from heaven's parts

Then a heavy topaz skate,

Does a looping figure eight.

Sanded off corundum vine,

Had red ruby roses nine.

But the pecking diamond hen,

Gets a perfect score of "10"!

Keywords: Education (general), Education - Precollege, Education - Undergraduate, Mineralogy and Crystallography

THE RHYMING PEG MNEMONIC DEVICE APPLIED TO LEARNING THE MOHS SCALE OF HARDNESS

A mnemonic device is a memory tool that allows the brain to remember information that would otherwise be difficult to recall. The basic principle of mnemonics involves using as many different stimuli to encode information as possible so that many different parts of the brain are involved in storing the event, thereby creating multiple pathways to retrieving the information.

Human brains evolved to code and interpret complex stimuli involving the five senses, spatial positions, emotions, and language. All these are used daily in modeling our sophisticated world and are stored effectively in memory. Unfortunately, some important geoscience information, such as the Mohs hardness scale, is presented to students as a colorless printed table to be memorized for future application in mineral identification. Although language is one of the most essential evolutionary human features, it is only one way humans learn and encode memories. This article will focus on applying effective mnemonic devices to learning important tabular information using the example of the Mohs scale for determining mineral scratch-hardness, one of the most useful properties in mineral identification.

MOHS SCALE OF HARDNESS

The hardness of a mineral is a measure of how tightly the atoms are held together within it. There are several tests for hardness that determine somewhat different properties. The Mohs scale, devised by German mineralogist Friedrich Mohs (1825), measures the scratch or abrasion resistance of a specimen compared to a standard set of common minerals. See Table 1 for the Mohs scale. Information on Friedrich Mohs and his other important contributions to mineralogy can be found in Staples (1964). If the point of a mineral of known hardness scratches a smooth, clean face of a specimen, the specimen is ranked as softer. By comparing the results of several scratch tests, the relative hardness of a specimen can be determined. Additionally, other common materials can also be used to gauge a specimen's hardness. These are also shown in Table 1.

Several factors contribute to the hardness of a mineral, particularly bond strength, and bond density, the number of bonds per unit volume in the structure. Bond density is important because the linkage of atoms across planar regions may be weak owing to an uneven distribution of bonds within the structure. Covalent bonds are very strong because atoms achieve attachment through electron sharing. Diamond, the hardest naturally occurring substance, has a three-dimensional covalently bonded structure. Ionic bonds are strong owing to the attraction of a positively charged electron-donor cation to its neighboring negatively charged electron-recipient anion. Smaller and more highly charged cations typically produce stronger bonds than larger or lower-charged cations. Metallic bonds occur when the outer shell of electrons is stripped, leaving positive ions closely packed together surrounded by electrons that hold the atoms together. In general, metallic bonds result in tough, ductile, plastic materials whereas covalently bonded and ionicly bonded substances are brittle. However, the hardness of metallic bonds varies over a wide range. Weak van der Waals bonds form between molecules that have a nonsymmetrical distribution of charge. The negative part of one molecule is attracted to the positive part of another, forming a weak bond. Talc, one of the softest minerals, exhibits van der Waals bonding between more tightly-bonded layers in its structure.