Shale and slate are two very similar types of stones found naturally along split bedding lines. The difference between these rocks can be difficult to pinpoint by looking at the stones. Slate is a more pressurised version of shale and, therefore, a little more durable. Shale is crumbly and usually breaks apart with the slightest amount of pressure. Because slate requires more pressure to break than the shale, it is used in landscaping and home projects as walkways.
Tap the stone lightly with a hammer or other hard object. Slate will sound slightly more metallic when hit. Shale has more of a "thump" sound.
Break the stone. Shale will crumble with very little resistance and break easily. Slate also can break without much pressure but will break into flat, thin pieces.
Pour water over the rock. Smell the rock while it is wet. Shale will smell like clay. Slate will not have a noticeable odour or smell only slightly like clay.
Examine the rock in the sunlight. Slate usually looks shiny and silky in the sun. Shale has a dull look.
Test the hardness of the rock. Both rocks are soft; however, shale is softer. Slate can scratch glass. Take a piece of the rock and scratch a mirror or piece of glass. You have to apply some pressure on the rock. If the glass scratches, you have slate.