The source of all kinds of energy with immence power, anyone who obtains it will be the ruler of the whole universe. The Silver Crystal is one of the most powerfull 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 wielder, it can cause him die if he use so much energy.
Depending on how it is used the Silver Crystal can eaisily be used to destroy an entire planet
Sailor Moon keep it on her necklace, but later is kept in her transformation brooch and in Moon Stick.
Queen Serenity told Sailor Moon that the Silver Crystal's true power depended on her heart.
Crystal was previously used and kept by Queen Serenity as heritage in Moon Dynasty, now kept by Sailor Moon as her pendant. Crystal revealed itself when Sailor Moon cried over Tuxedo Mask dead body and heal him.
Its first power which was revealed was healing and reviving from dead, used on Tuxedo Mask. Crystal seems to have some kind of its own will as it was 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 a future version of the Silver Crystal. If both crystals touch each other the world would be destroyed. Also, in Act 26, when Sailor Pluto dies her tears morph into her very own crystal, the Pink Moon Crystal.