where slate comes from

Have you ever wondered where slate comes from

Slate comes from all over the world, from the U.S. to Brazil to China to India and throughout Europe as well as many places in Africa.  Australia has even recently started to mine for slate.  You have to dig very deep down past the soft "top rock" to get to good stone,  producing the product is a skill in itself. Putting it in is an art as well, make sure you have the right  contractor with a slate and tile background.
Have you ever heard of ribbon slate
Ribbon slates are Pennsylvania black slates that have small bands running through them. These ribbons contain a high amount of carbon that deteriorates much faster than the rest of the slate. This results in the slate becoming separated at the ribbon, allowing either the slates to fall out or water to penetrate the roof.They still last 50 to even 100 years if the roof is steep and well shaded. Once the ribbons become soft, the roof  must be replaced.

The grading system for slate
S-1 means the slate will last more than 75 years. S-2 slate is meant to last 45 to 75 years and S-3 slates are meant to last 45 years or less.
The different colors of slate
Gray, green, purple, black, and red. You can make a good looking roof by mixing a couple of these colors together too. Just ask your slate or tile roofing contractor, the most common being gray-black, gray-green, and green-purple.
will the color change over time
Weathering or semi-weathering green and gray slates can develop brownish and pinkish tints, due to iron in the slate. At the time of new installation, the percentage that will turn color is unpredictable. It can be as little as 5 to 10 percent or nearly 100%. The only way to keep the color from changing is to get slate that has come off another roof that has already weathered.