Just like the shell of a clam, a pearl is composed of calcium carbonate (mainly aragonite or a mixture of aragonite and calcite). in minute crystalline form, which has been deposited in concentric layers. The ideal pearl is perfectly round and smooth, but many other shapes, known as baroque pearls, can occur.
Rimula is a genus of fungi in the Helotiales order. The relationship of this taxon to other taxa within the order is unknown (incertae sedis), and it has not yet been placed with certainty into any family. ^ Lumbsch TH, Huhndorf SM. (December 2007). Outline of Ascomycota â 2007.
1 The macula is a small but vital area of the retina at the back of your eye. 2  It is about 5 mm in diameter. 3  The macula is the part of the retina that is the most densely packed with rods and cones. 4  The macula is essential for central vision. The macula is a small but vital area of the retina at the back of your eye. 2  It is about 5 mm in diameter. 3  The macula is the part of the retina that is the most densely packed with rods and cones. 4  The macula is essential for central vision.