Alright, all this amazing talk about natural hones is making me want to go rock hunting!!! I'm in Nova Scotia and it's full of lots of different rock structures. There seems to be an abundance of 'shale' which is similar in its properties to slate.Shale and slate are both metamorphic materials and the two terms are sometimes use interchangeably, but the materials are not the same. Many of the items sold today for landscaping (flagstones, retaining walls) and construction (chalkboards, roofing tiles, pool tables, etc.) uses as "slate " is actually the much more inferior form—shale. Shale is metamorphic clay-like sediments, lightly compacted into thin, crumbly layers. It may contain high concentrations of quartz, feldspars, pyrites amorphous silica, and clay minerals: illite, kaolinite, chlorite and smectite (montmorillionite). This smectite clay is a highly absorbent component that can swell to several times it's normal size, making the shale loose strength. Slate on the other hand is much stronger and does not absorb water (remember how fast those school blackboards would dry when you had to stay after class?) Generally, it has much greater strength. However, certain types of slate still may be less than desirable. There also is a high calcite/dolomite form of slate called Marl Slate, from Durham, UK, which can be softer and easily attacked by acids.If i'm looking at 'slate' or 'shale' is anything that is surface exposed going to be good enough? I'm going to try to find a few pieces that are CLOSE to being flat and test them out on a junker to see what I come up with!Any tips (MichaelC) or others, would be appreciated :)
