The boulder is a crystalline rock consisting of pyroxene (chrome-diopside), garnet, and a little olivine, and is studded with diamond crystals; a portion of it is preserved in the British Museum (Natural History).
The pyroxenes may be pale green diopside, dark green aegirine-augite, or blackish green aegirine (soda iron pyroxene), and in many cases are complex, the outer portions being aegirine while the centre is diopside.
Both Great and Little Ararat consist entirely of volcanic rocks, chiefly andesites and pyroxene andesites, with some obsidian.
The rocks are liparites, dacites, hornblende and pyroxene andesites.
Quincy granite, a hornblende, pyroxene, bluish or greyish, without mica, was used for the construction of the Bunker Hill monument at Charlestown (in 1826), and of King's Chapel, Boston; and for interior decorations it has found some use, for example in the Philadelphia city buildings.