- "But not until the End, when Fëanor shall return who perished ere the Sun was made, and sits now in the Halls of Awaiting and comes no more among his kin; not until the Sun passes and the Moon falls, shall it be known of what substance they were made."
- —The Silmarillion
It appeared like the crystal of diamonds, yet was stronger than adamant, and luminescent by its own composition. Its actual ingredients were known by none but Fëanor. It is also said that "no violence could mar it or break it" in all the Kingdom of Arda.
Sil- is a Sindarin term meaning "shine" or "white".