Answer:
Old people and owls are said to be this.
Nothing specific, but more than a few. This many clustered, together will do.
What can you never get rid of when you lose it?
My second is performed by my first, and it is thought a thief by the marks of my whole might be caught.
Ancient and majestic, great big piles of stones, Used to encase both riches and bones. Seen from certain angles, They look like big triangles.
It flows out of the soil, It burns you if it boils, And holds us in its coils, More valuable than gold, As black as it is old.