More detailed analysis of collected sand is conducted in the laboratory.

We will do more detailed analysis of the sand samples you collected in the field back in the laboratory. First, sieve bulk samples to remove particles coarser than 250μm (1 μm = 1/1000 mm). Coarser particles tend to contain more lithic fragments rather than single crystal mineral. Next, prepare thin sections of the sieved bulk samples and the heavy mineral-concentrated panned samples.

Samples of rock and minerals mounted on slide glass and ground down until very thin are called thin sections. Very thin samples of most minerals, except those that are opaque, will become translucent and therefore can be observed under a microscope.

• Bulk samples collected in the field are put through a sieve, removing particles coarser than 250μm
• Isolated heavy mineral samples are further concentrated and purified using heavy liquids (heavy liquid separation).
• Left alone, sand samples will scatter, so they are mixed with epoxy into a paste, then affixed to a slide glass.
• 4. Once the epoxy has set, samples can be ground down to a thickness at which they can be observed.

＊What is Heavy Liquid Separation?
Liquids that are denser than water are known as heavy liquids. The density of light minerals is in the range of 2.6-2.7 g/cm³; such particles will float in a liquid with a higher density. Heavy minerals, on the other hand, have a density of 3.0 g/cm³ or more. Therefore, if the density of a liquid is adjusted to between 2.6g/cm3 and 3.0 g/cm3, then light minerals will float and heavy minerals sink in it. This process, known as heavy liquid separation, is commonly used to isolate minerals.

A special kind of microscope, known as a polarizing microscope, is used to examine thin sections. Microscopic analysis allows us to examine the details of mineral species and textures not visible to the naked eye or through a hand lens.

Some minerals are difficult to distinguish with an optical microscope. Such minerals are differentiated through an analysis of their chemical compositions, conducted under an electron microprobe. Some minerals have wide variety of chemical composition. For example, the chemical formula for orthopyroxene is (Fe, Mg)₂Si₂O₆.The first part, (Fe, Mg)₂indicates that the combined quantity of iron (Fe) and Magnesium (Mg) atoms will sum to 2. In other words, orthopyroxene may have an iron-magnesium atomic ratio of 1 to 1 or 0.5 to 1.5, and still be orthopyroxene. Such compositional differences often reflect the different origin of minerals. The electron microprobe brings these minute differences to light, allowing us to infer the origin of each mineral.

Minerals such as zircon and monazite contain minute amounts of radioactive elements such as uranium or thorium (in, of course, such tiny amounts that they are harmless to humans). These elements or parent nuclides, were incorporated when the mineral formed and slowly break down over time, transforming into daughter nuclides, in a process known as radioactive decay. Because radioactive decay occurs at a constant rate, scientists can observe the amount of radiation being produced and the volume of daughter nuclides to determine how many years ago (more realistically, how many millions and billions of years ago) the mineral was formed. Thus equipped with an extremely accurate internal clock, these particles are valuable assets in determining the origin of a mineral.

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