Magnetism in Gemstones
An Effective Tool and Method for Gem Identification
Diamagnetic Response (blue Topaz)
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It's interesting to note that gemstones which do contain detectable paramagnetic metal ions have a push-pull relationship with the magnet. They are simultaneously diamagnetic, with most of the gem’s chemical composition being weakly repelled away from the magnet, and paramagnetic, with trace impurities of metal ions dispersed throughout the gem being attracted toward the magnet. In most cases, the pull force is strong enough to overcome the repel force. In rare instances, a weak paramagnetic pull will be exactly balanced by the weak diamagnetic repulsion, and the gem will show no response to a magnet in either direction. This is the truest example of an inert response, but we refer to both this response and the much more common diamagnetic response as "inert".
About a third of all gem-quality minerals are diamagnetic and show a weak repulsion to a magnet. Not all are colored by light diffraction, color centers or other color-producing processes. Some simply have very low concentrations of metallic chromophores such as iron or chromium. The repel responses of diamagnetic gems help us separate them from gem types that are attracted to a magnet. To use the same terminology used for gem fluorescence, we refer to a negative or repel magnetic response as inert (not attracted to a magnet). Throughout this website we use the terms "inert" and "diamagnetic" interchangeably.
Diamagnetic (Non-magnetic) Gems
Some gems, such as "prescious" Opal and Topaz, are not colored by paramagnetic metal ions. Their color is due to processes such as light diffraction from tiny spheres of silica (ex. Opal), or defects in the atomic structure of the crystal that give rise to color centers (ex. Topaz). Irradiation is often involved in the production of color centers. Gems colored in these ways are "non-magnetic" or diamagnetic, meaning they show no attraction to a magnet. Instead, they are repelled by a magnet when floated on a raft in water (see video below).
Most solid substances from glass beads to jelly beans are weakly repelled by a magnetic field. These substances don't contain enough unpaired electrons to create magnetic attraction. A repel response indicates Diamagnetism, a type of magnetism in which the induced magnetic field opposes the applied magnetic field of the magnet. All diamagnetic responses in gems are extremely weak, and the repel force is fairly constant among different gem types. The extreme sensitivity of our magnetic wand and floatation method makes it possible for us to observe the diamagnetic responses of gems.
We will loosely use the term primary gemstone when referring to the gems that are most commonly found in jewelry, such as the species mentioned above. About 200 types of minerals produce gem-quality crystals, and of these, only about 20 to 40 minerals account for all the primary gems fashioned into jewelry. Many gems referred to as secondary gemstones are fashioned from minerals that are too soft, fragile or rare to be used in most jewelry, or are not consistently available for jewelry. Fluorite, Apatite, Kyanite and Calcite are examples of secondary gems that are typically diamagnetic. These gems rank low on the hardness scale and are therefore easily scratched. For introductory gem identification, we are more concerned with the primary gems.
Some diamagnetic gems that can derive all or most of their color from color centers include Diamond, Zircon, Spodumene and Quartz. The varieties of Quartz with color centers are Amethyst, Citrine and Smoky Quartz. All these gems show magnetic repulsion rather than attraction.
Paramagnetic metal ions are often trapped in color centers in gems, but the concentrations of these metal ions are too low to be detectable with a magnetic wand. Strong gem color can sometimes be induced by color centers when metal ions are present in only a few parts per million.
Weakly Magnetic Madeira Citrine
A rare exception in Quartz are certain Citrines that are colored by iron impurities rather than (or perhaps in addition to) color centers, such as some natural red Madeira Citrines from Brazil, and on rare occasions even yellow Citrines. These rare Citrines can be weakly magnetic.
Gems of organic origin such as Pearl, Ivory, Amber, Coral, Shell and Jet are not colored by paramagnetic metals. All organic gems are inert (diamagnetic).
Below is a list of the 20 most common gems that are typically inert (diamagnetic). In a few of these cases, such as Apatite, Calcite and Glass, gems are occasionally weakly magnetic due to metallic coloring agents. In other diamagnetic gems such as Quartz and Opal, macroscopic and microscopic inclusions can result in magnetic attraction (paramagnetism).
20 Common Diamagnetic Gemstones
This Citrine Shows a Diamagnetic Response