{
    "variants": {
        "variation=tiny": { "model": "rocks:block/tiny_gravel_rock" },
        "variation=small": { "model": "rocks:block/small_gravel_rock" },
        "variation=medium": { "model": "rocks:block/medium_gravel_rock" },
        "variation=large": { "model": "rocks:block/large_gravel_rock" }
    }
}