A good example should tick the boxes of:
~ Unique shape: some people prefer fantastically shaped perforated forms resembling smoke or a skeleton
~ Resemblance: if it resembles a famous mountain all the better!
~ Texture: something to rest your eyes and hands on, take a break from your spreadsheets and get tactile!
~ Colour: no need to explain
~ Sound: a stone or metal one should have a nice ringing tone when gently struck