Highly unusual and rare 'Herkimer sphere' Quartz. It is believed that these grew in vesicles in hydrocarbons. Besides the rounded form, another unusual feature are the small flat crystal faces - I count five such faces on this specimen. You can read more about this unusual occurrence at the following link: http://www.herkimerhistory.com/QuartzSpheres.html. According to this website, the largest such sphere found to date (by 2009, the time the web page was written) was 1.o cm across. Since this one is 50% bigger than that, it is likely that this sphere is in the top percentile for size. Lustrous and undamaged. A superb rarity for a Quartz collector.