The Silver Crystal is the source of all kinds of energy with immense power, anyone who obtains it will be the ruler of the whole universe. The Silver Crystal is one of the most powerful magical items in Universe using power of it wielder's own life force in various effect. Its able to heal entire world, but because its using life force of it's wielder, it can cause them die if they use so much energy.
Depending on how it is used the Silver Crystal can easily be used to destroy an entire planet. Sailor Moon kept it on her necklace, but later is keeps in her Crystal Star. Queen Serenity told Sailor Moon that the Silver Crystal's true power depended on her heart.
The Silver Crystal revealed itself when Sailor Moon cried over Tuxedo Mask's dead body. Its first power was revealed to be 'healing and reviving the dead' it was able to revive Tuxedo Mask when used on him. The Silver Crystal also seems to have some kind of its own will as it is able to protect Sailor Moon from being hurt.
The lifespan of the Silver Millennium family is about 1000 years. The rate of aging halts after adulthood due to the power of the Silver Crystal. After King Endymion and Neo Queen Serenity took the throne in the 21st century an era of long life begun in Crystal Tokyo. Now nearly everyone on Earth has gained humanity's greatest wish, long life.
Second Silver Crystal
Chibiusa possesses the future version of the Silver Crystal. If both crystals were to touch each other the world would be destroyed.