Like a dandelion blooming in your yard, this stone in glass is an unwelcome addition to a glass container. The smooth grey surface belies extremely high tensile stresses in the surrounding glass, created by the stone’s lower coefficient of thermal expansion. Silicon balls such as this stone are created when aluminum contamination in the cullet reacts with the glass melt, creating elemental silicon and aluminum oxide. When the aluminum oxide dissolves, only the silicon sphere remains. The high induced stresses sometimes cause spontaneous cracking, such as in this stone, or spontaneous fracture sometime during processing. For that reason, silicon balls are among the very worst of stones!