These samples of pectolite are displayed in the Smithsonian Museum of Natural History. Pectolite is an silicate mineral of calcium and sodium. It has the composition NaCa2(HSi3O9). The rounded specimen has a diameter of about 11 cm wide and is from Prospect Park, New Jersey.
From the museum's description: "The rounded shape of pectolite comes from many crystals crowding together like seeds on a dandelion. You can see some in the broken area of the specimen. The other rounded, or botryoidal, specimens formed in much the same way."