Ultrabasic rocks. The largest measures approximately 19x12x11 cm. and it has slickened sides. The rest are a bit more weathered and their sizes range from 8x6x8 cm to 4x3x4 cm.
Cite the IMLGS database as: Curators of Marine and Lacustrine Geological Samples Consortium. The Index to Marine and Lacustrine Geological Samples (IMLGS). National Geophysical Data Center, NOAA. doi:10.7289/V5H41PB8 [date of access].