Since the conch is the instrument that first brings the boys together on the island, it becomes a symbol of unity. It is also a natural object, almost like a beautiful gem Ralph and Piggy discovered; so it has an association with a natural beauty and a natural order. Therefore, there is something natural about using it to establish order but it is also a social object because it is used to organize the society of boys on the island. It is a symbol of natural and social unity and organization.
As time goes on, the conch is used when a boy wishes to speak. Given that the leaders do most of the speaking, the conch becomes a symbol of power. He who holds the conch has the power to speak and possibly give orders. When the boys splinter into two groups, the conch loses both of these associations: unity and power. It no longer can be used to unify all of the boys and the boys no longer use it to establish power in an orderly way. The significant moment when the boys abandon a civilized society occurs when Piggy is killed and this is also when the conch is shattered.
The rock struck Piggy a glancing blow from chin to knee; the conch exploded into a thousand white fragments and ceased to exist. Piggy, saying nothing, with no time for even a grunt, traveled through the air sideways from the rock, turning over as he went.
Suddenly Jack bounded out from the tribe and began screaming wildly. “See? See? That’s what you’ll get! I meant that! There isn’t a tribe for you any more! The conch is gone—”
In the end, the conch became the symbol of the tribe itself.