tumbled brown and black turitella agate chalcedony crystal

agate black black background brown chalcedony close closeup crystal dark decorative fossil gem gemmological gemmology gemological gemology gemstone geological geology gray isolated jasper macro macro shooting mineral mineralogy minerals natural nature pebble polished rock semi-precious semiprecious shell silica silicate silicium dioxide small snail specimen stone surface texture tumble tumbled turitella turritella turritella white