Mining

Mining is an activity that generally becomes available once you have a shovel and a pick.

Topography
The topography of the world is rather predictable. Any pick will suffice for mining stone, although picks do have depth restrictions based on the durability of the pick.

Shafting
There are three ways to shaft: a vertical drop, a 45 degree slant, and a horizontal branch. They have their own advantages and disadvantages.

Horizontal Branch
The horizontal branch does not increase depth, so you will be unable to find more valuable metals and gems. However, going back is easy and does not require any sort of climbing mechanism such as stairs or ropes.

Slant Mining
The slant mine increases depth. Going back requires either a staircase (which costs 6 rocks) or 1 cord of rope. Note that this is a one-time cost, and additionally you only have to create an access route starting depths at least 3.

Vertical Mining
There is a risk for vertical mining in deeper depths, which is falling into lava. However, an advantage is that you do not need to light up the way in order to uncover new materials (due to the light falling directly above you). Going back requires a larger expenditure of a vertical staircase (10 rocks) or 2 cords of rope.

Materials Found
Materials are uncovered by providing a sufficient lighting source.

Materials are described fairly vaguely and until you get a better method of classifying minerals you get these vague descriptors:

By Color
You can identify minerals by how hard they are (based on pick strength) as well, or how deep you find them.

By Depth
You can also identify them if you have a classification tool. Typically, more valuable minerals are found deeper.