A. Technically, a millimeter is 1/1000th of a meter. It is a tiny unit of measurement. If you are not familiar with the metric system, we suggest that you look for a yardstick, tape measure, or ruler in your house. Chances are that the metric system of measurement will be shown on the device, on the side opposite inches and feet. The smallest units are millimeters; the numbered units are centimeters which are groups of 10 millimeters.

The two measurement systems are really not compatible; but the following approximations can be useful. Three millimeters is just a tad larger than 1/8 inch. Five millimeters is approximately 5/16 inch. A typical pencil eraser is roughly 7 mm.

A. A carat is a unit of weight equalling .2 grams. It is NOT a measurement of physical size.  A gram is defined as the weight of one cubic centimeter of water.

Many shoppers try to compare a 1 carat colored gemstone to the more familiar 1 carat diamond; but the comparison doesn't give an accurate picture. Colored gemstones can be and usually are heavier or lighter than diamonds. Additionally, colored gemstones are not necessarily cut with the same depth as a diamond. Both of these factors can contribute to an erroneous estimate of size.

A. How long is a piece of string? How many ounces in a bottle? All of these questions are really impossible to answer, as the inquiry itself does not contain enough information!

Carat is a measurement of weight; millimeter is a measurement of dimension or distance. Gemstones vary dramatically in weight. Diamonds are far heavier than emeralds; cubic zirconias are far heavier than diamonds. Hence, a 1 carat emerald is larger than a 1 carat diamond, and a 1 carat diamond is larger than a 1 carat cubic zirconia.

A. Absolutely! Synthetic (which is the same as man-made) stones are chemically identical to natural stones; but, of course, they were made by man and not mined from the ground.

Simulants (which is the same as imitation) stones have nothing in common with the natural gemstone they imitate, save for the color and possibly general appearance. Hardness, weight, durability, and optical properties will all be different.

A. No. Many genuine gemstones can be so similar in appearance to each other that it's virtually impossible to identify them by color alone.

For example, a deep red stone may be a ruby, a rubellite tourmaline, an andesine, a pyrope garnet, a spinel, a red diamond, or other precious stone! It may also be a glass or plastic simulant.

Various tests are available for identifying gemstones, but no single inexpensive instrument or easy test will identify all stones without question.