Inclusions are internal features of gemstones that may be comprised of either solids, liquids, or gasses that became entrapped in the crystals as they grew.  Inclusions may also consist of cleavages, cracks, and fractures that formed as the crystal was growing.  While some regard inclusions as flaws, they may also be valued for the interest they lend to a stone.  For instance, the stars in star rubies and sapphires are caused by needle-like crystals of rutile which formed parallel to the faces of the host corundum crystals.  When these gemstones are cut into a cabochon (domed, with a polished surface), light reflecting from these internal needle-like inclusions create a cat’s-eye effect (chatoyancy) or star stones (asterism).

 

P.S.  Inclusions with the appearance of water-lily leaves are typically found in peridot from Arizona.