Gems assist and magnify magic.
There are four shapes of gems: crystal, teardrop, sphere, and oval. The shape has nothing to do with magic power neither does the color.
Gems glow slightly all the time and more so when magic is being used. They can come in any color and the gem color can differ from the color of their glow.
Everything else-
Cracked and broken gems are unstable and can cause magic to backfire, be too strong, too weak, unfocused, not work, and even kill the user. Only incredibley powerful force/magic can break or crack BD gems; it requires even more power to destroy them completely. The stronger a BD is the more power it takes to crack/break/destroy their gems, the weaker they are the less power is needed. Removing a BD's gems requires a specific ritual and more magic power than it takes to destroy them. Removing gems is considered as taking their life force and/or magic, so it is forbidden and performing the ritual will bring about the penalty of death[cont]

(cont) The size of the gem varies however they are never bigger than their dragon's largest claw. Gems extend/start most commonly from the horns or spikes around the head;they can also wrap around the ends of the tail, ankles, and wrists. Wrapping around or starting/extending from any other parts of the body is uncommon but possible. When Gems are removed via ritual they can be used to forge weapons, magical items, and armor, the item(s) forged with the removed gems have ( depending on how many where used and how powerful the BD is/was) some/half/all of the magical power the BD they were taken from had/has. The items, if made correctly, are almost as strong as the gems themselves. When a BD dies the gems cease glowing, become dull, and no longer are able to be used in magic or used to forge forbidden items, so in other words are useless to the living and dead. Removed gems retain their magic even after the original owner has died. The starting point of a section of gems cannot be (cont

cont) moved to another point/spot. BD's have control over their gems and can move them to wrap around things, pick up, or attack. The gems have pain nerves only to the extent that the BD can feel pain when they are broken or destroyed. If a BD has a broken gem they can choose not to use that one in spells/magic that do not require it's power or the number of gems that includes more than they have without it.
End.
BD means Bloomdragon
sorry if it's confusing I typed it the way I wrote it. Any questions?