An interesting aspect of the nature of gems within Tolkien’s work is that it is very difficult to determine whether they are meant to be good or bad. Gems play a very prominent role throughout Tolkien’s universe, from the Silmarils to the Rings of Power to the “living gem” of Lothlorien. Though the gems themselves never have any will of their own (unlike the One Ring), certain gems seem to have an effect over people that can drive them to do bad things.
Throughout Tolkien’s work, gems are very much associated with life. After Morgoth and Ungoliant destroyed the Trees of Valinor, it was said that the only way to heal them would be to break open the Silmarils. The Three Elven Rings all contain a gemstone, and their primary power is in healing and preservation of life. Elrond, the bearer of one of the Rings, was said to be the most powerful healer in all Middle Earth. The Seven Rings for the Dwarves and Nine for Men all had powers, which, among other things, extended the lives of their bearers. Although the gems did not give new life, their bearers were able to live for unnaturally long lifespans.
Additionally, gems are associated with light. The Silmarils, which contained the light of the Trees, were said to shine with a light of their own, as well as reflecting the brilliance of any light that fell upon them. The Arkenstone in The Hobbit was said to have this property as well. When the Fellowship was in Lothlorien, a light shone on the finger of Galadriel, who was wearing one of the Elven Rings. The Phial of Galadriel, though not a natural gemstone, shone with the light of Earendil.
In the Third Age, gems seem to be primarily associated with people who do acts of good. The Three Elven Rings are used by their bearers to preserve and protect the beauty in the world against the blight of Sauron. The Rings are never used for ill, and their beauty and power do not cause people to become obsessed. The Arkenstone, though it was on some level obsessed over by Thorin, resulted in the quest to retake Erebor and return of the Dwarves to their stolen homeland. Galadriel gives Frodo a phial containing the light of Earendil, in effect a Silmaril containing the light of the Trees of Valinor. This “gem” does not have the corruptive properties of the Silmarils however, and Frodo and Sam are able to use it in times of need without succumbing to lust for it. The Rings of the Dwarves, though eventually leading them to lust and greed, did not allow Sauron to impose his will upon them. The effects merely amplified the greedy nature of the Dwarves rather than being used to cause evil, and the Dwarves were able to use these gems to increase the wealth and prosperity of their people.
However, in past ages gems were not so purely good. For instance, Feanor coveting the Silmarils above all else caused him to refuse to heal the Trees of Valinor, go to war against Morgoth, kill the Teleri and steal their ships, and many other atrocities before his eventual demise. Though the gems coming into contact with anything evil would cause that being to be burned, something seemingly good, they were lusted after excessively by those who saw their beauty and radiance. The Nine Rings of Power that were given by Sauron to kings of men most likely also had gems in them, as they were very similar to the Seven for the Dwarves. These Rings allowed for Sauron to eventually take the men completely under his dominion and control their minds as their bodies wasted away and they became wraiths. These gems clearly served a very ill purpose.
It is very interesting to note, however, the role of the Silmarils in the Second Prophecy of Mandos concerning Dagor Dagorath, the Final Battle. In this Prophecy, Morgoth will return and destroy the Sun and Moon. After Morgoth is killed by Turin Turambar, all of the Silmarils will be returned to the Earth and Feanor’s spirit will be released and he will break them to release their light and return life to the Trees of Valinor. The fact that Feanor would at that time be willing to destroy his most prized creations and use them for good means that their corruptive properties are perhaps not necessarily universal.
An interesting side thought that I had was related to our discussion of the nature of Lothlorien and the Mallorn trees there. The trees turned the realm into a living gemstone, with Galadriel at the center. They have silver bark and in the autumn the leaves turn gold, and when they fall they carpet the ground in gold. The scene in which the Fellowship enters Lothlorien describes the river as “crystal” as well. Galadriel is the center of the forest and the giver of light. There are no blemishes or decay, and in class the forest was described as a representation of paradise. This seems strange to me, however, knowing the nature of the Mallorn Trees and the fact that they came from Numenor. It is said that the Mallorns of Numenor grew to greater heights and to be more beautiful than those that Galadriel was able to cultivate in Lothlorien. It seems strange to me then that Lothlorien would be a representation of paradise when Numenor, the land that fell into darkness and was swallowed by the sea, was even more beautiful.