Compressed Blocks

Compressed Blocks can be enabled/disabled in the config and custom compressed blocks can be added for anything that you want.

Each compressed block has the combined hardness of all blocks stored in it. This makes it very hard to break anything past about 4x. The Multi Tool is your friend there.

As for the texture on the blocks they are dynamically created using your current texture pack. The max resolution can be set in the config, just be warned setting it to high can break Minecraft's texture mapping.

Some examples: