Small and worn close to the heart, I open to reveal what you keep dear. A tiny place for memories or faces. What am I?

A pendulum pivoting around a single point, out on yonder playground as a popular pastime. Ah, how the youths propel themselves to such ponderously great heights.

I’m part of you, but not quite seen. Break me once and you’ll know what I mean.

Crystal fingers dripping light, I bloom in ballrooms every night. From ceiling high, I flare and glare, A sparkling crown suspended there.

I can be kept, I can be broken, I am mightier than any sword, and yet, add one letter to me, and a sword is exactly what you’ll find. Now, then, what am I?