Yellow Calcite is associated with the solar plexus, self-confidence and hope. Also, a great prosperity stone!
They are about 3 inches by 1.5 inches (all shapes vary). And they weigh approx. 4 ozs. 
Yellow Calcite is a stone for those who wish for greater positive energy, to work with happy & blessed vibes, and wake themselves to a more positive state of mind. Yellow Calcite is a stone of joy, confidence, and motivation which helps us to examine our hidden potential and unlock it in order to pursue the successes and opportunities that await us. An excellent stone for the purposes of Manifestation, it allows for greater focus on our intentions, helping us to visualize our goals and dreams to better crystalize them into existence. Extensive work with this Calcite will prompt you to trust your instincts and intuition, strengthening your hidden knowledge.