Block 2D icon

Step 1

Create the 2D icon for the block

Replace myitems with your namespace!

info:
  namespace: myitems
items:
  rocks:
    display_name: Rocks
    permission: blocks.rocks
    lore:
     - 'lore-decorative-item'
    resource:
      material: PAPER
      generate: true
      textures:
      - item/rocks
    events:
      interact:
        right:
          set_block:
            block: rocks_placed
            target: RELATIVE
            decrement_amount: true
        right_shift:
          set_block:
            block: rocks_placed
            target: RELATIVE
            decrement_amount: true

Now create the rocks.png file inside the folder contents\myitems\resourcepack\myitems\textures\item

Step 2

Create the item which shows the placed rock model. It is a different item form the one you see in the inventory (the one created in the step 1).

info:
  namespace: myitems
items:
  rocks_placed:
    display_name: ""
    permission: admin.blocks.rocks_placed
    resource:
      material: PAPER
      generate: false
      model_path: block/rocks_placed
    specific_properties:
      block:
        placed_model:
          type: REAL_WIRE
        cancel_drop: true
        sound:
          place:
            name: block.stone.place
    events:
      placed_block:
        break:
          drop_item:
            item: rocks
  rocks:
    display_name: Rocks
    permission: blocks.rocks
    lore:
     - 'lore-decorative-item'
    resource:
      material: PAPER
      generate: true
      textures:
      - item/rocks
    events:
      interact:
        right:
          set_block:
            block: rocks_placed
            target: RELATIVE
            decrement_amount: true
        right_shift:
          set_block:
            block: rocks_placed
            target: RELATIVE
            decrement_amount: true

Now create the placed_rocks.json file inside the folder contents\myitems\resourcepack\myitems\models\block\

Done!

Now try to right click with the rocks item and you will see it places the rocks_placed model.