The Minecraft Wiki will likely provide you with better answers than a forums Q&A: "Mined blocks drop themselves instead of the usual items Allows collection of blocks that are normally unobtainable. Items which can be obtained legitimately only through use of Silk Touch: coal ore, cobweb[until 1.9], diamond ore, emerald ore, grass block, huge mushrooms, ice, lapis lazuli ore, mycelium, podzol, packed ice, nether quartz ore and redstone ore. Additionally ender chests, after they are placed, can only be retrieved by a pickaxe enchanted with Silk Touch. Doesn't work on: cake, carrots, cocoa pod, double slabs, fire, farmland, melon stems, monster spawner, nether wart,potatoes, pumpkin stems, snow layers, sugar cane, wheat and inverted daylight sensors. Gravel harvested with a silk touch shovel will never yield flint. This is due to the fact that silk touch bypasses the rare harvest RNG entirely."