"The Heart Cockle seashells (Corculum Cardissa) are naturally in the shape of a heart. Also known as the True Heart shell the Heart Cockle is a bivalve. This seashell is very delicate and when the upper and lower shells are joined together they form a heart shape. These are very lightweight shells."
Iceland spar is a clear, transparent, colorless crystallized variety of calcite (calcium carbonate, CaCO3). Large pieces are split along natural cleavage planes to form natural rhombs. Iceland spar is probably best known for exhibiting the optical property of double refraction - so, anything viewed through the crystal appears double.