There are a few Minecraft Blcoks that are special or have Special Properties.

Glass - Very transparent and seethrough. Lets light go through.

Leaves - Slightly transparent and seethrough. Lets light go through.

Ground/Grass - If light is shined on ground, grass grows ontop. Gras is removed when light is taken away.

Flowers and Mushrooms - Flowers need sunlight to grow. They also need to be ontop of ground or another flower to survive.

Sand and Dirt - They are both affect by gravity.

Water - A block that is normaly not able to be placed by a user. It spreads across the X -plane and spreads down the Y - plane when possible very quickly. MOvement through water is slow. You can travel up in water without hacks.(Note: Modded water that is placed in World of Minecraft does not spread and is not removed by sponges. It can only be removed by building ontop of it.)

Sponge - Removes the water around it in a 3x3 square

Lava - A block that is normaly not able to be placed by a user. It spreads across the X -plane and spreads down the Y - plane when possible very slowly. Movement through lava is very slow. You can travel up in lava without hacks.(Note: Modded lava that is placed in World of Minecraft does not spread. It can only be removed by building ontop of it.)

Ores - Ores cant normally be place by a user. They can be placed in World of Minecraft servers.

If there are any ones I have missed comment about them