ActuallyAdditions/src/main/resources/assets/actuallyadditions/blockstates/block_quartz_slab.json

{
  "forge_marker": 1,
  "defaults": {
    "model": "minecraft:half_slab",
    "textures": {
      "bottom": "actuallyadditions:blocks/block_misc_black_quartz",
      "top": "#bottom",
      "side": "#bottom"
    },
    "transform": "forge:default-block"
  },
  "variants": {
    "normal": [{}],
    "inventory": [{}],
    "half": {
      "bottom": {},
      "top": { "model": "minecraft:upper_slab" }
    }
  }
}