This is double slabs. . . This pack allows you to build with new blocks, by taking advantage of the special feature that can be done with double slabs.
When placing two slabs on top of each other it creates a double slab. Which we can make a custom texture for to kind of give us new blocks.
This pack adds a large variety of those, from the three stone types to the sand stones and the prismarine types. With many more to come in the future. Wanna give some feedback to the author, join this convenient discord server and check out all his other stuff while your there too