The Stones of Sinnameron are all the products of the master gemsmith Sinnameron.  In fact, they are his finest creations.  They are a set of several stones, all cut from the same parent gem.  They all are of similar size, and have a distinctive cut.  It is thought that the Stones were originally part of the same piece.  Currently, the Stones are all in different settings.  Rings, pendants, brooches, earrings, etc.  They have been spread across the known world, and are in the possession of many different owners.  It is very improbable that the owners have any idea of what they possess.  Of course, many collectors would pay a princely sum to possess the complete set.
But that is not the main reason these stones are important.  The Stones of Sinnameron have been known to find their way into the keeping of people destined to become heroes, and bring them together.  A handful of sages know of this property of the Stones, and some make it their business to find the chosen ones.  Others want to use the Stones to identify potential threats.

Magical Properties:

The Stones will sometimes find thier way into the possession of those destined to become heroes.  Either through inheritance, purchase, finding, or outright theft, they will be found with destiny’s favorites.  No one knows when the Stones will point to a group of heroes, although some think that the Stones will make that obvious.  Keepers of the Stones will be drawn to one another.  It is possible that Keepers will not have any knowledge of the Stones or their properties.  They might not even realize that they belong with one another.  It is not known whether or not Sinnameron purposefully enchanted the Stones to behave that way, or if it is an inherent property of the Stones themselves.