The pyramid is a symbol of positivism, achievement and unity. Helps to access the unknown universal knowledge and have the wisdom to understand it. It is a powerful thought amplifier. 
Black Obsidian Stone is a powerful cleanser of psychic smog created within your aura, and is a strong psychic protection stone. It has powerful metaphysical properties that will shield you against negativity, and their energy may stimulate the gift of prophecy. It an excellent crystal to use when you have been doing spiritual or healing work as it grounds you to Mother Gaia.
Size and Shapes will vary as these are handmade.