The border on the Quartz Block texture are blending into the Smooth Quartz texture, but only on the lefthand size, taking away the hard edge that would separate the two blocks when put together.
[media]The border on the Quartz Block texture are blending into the Smooth Quartz texture, but only on the lefthand size, taking away the hard edge that would separate the two blocks when put together.
[media]
This also applies to dark prismarine in the texture update, see MC-165933