Shiva Lingham Yoni Egg
Great for balancing the masculine and feminine.
This stone holds within it the feeling of unity and duality.
On one hand you see the masculine part of the stone within its phallic shape, and the feminine as well in the egg shape, and in the beauty of the markings on the stones.
The stone as a whole recognizes that they are one, yet they are each a separate entity within the one. Its vibration has a different action depending on where you place it.
(description from: https://www.healing-crystals-for-you.com/shiva-lingam.html)