Slate can also contain abundant quartz and small amounts of feldspar, calcite, pyrite, hematite and other minerals. Most slates are gray in color and range in a continuum of shades from light to dark gray. Slate also occurs in shades of green, red, black, purple and brown.The color of slate is often determined by the amount and type of iron and organic material that are present in the rock.The tectonic environment for producing slate is usually a former sedimentary basin that becomes involved in a convergent plate boundary.he color of slate is often determined by the amount and type of iron and organic material that are present in the rock. The tectonic environment for producing slate is usually a former sedimentary basin that becomes involved in a convergent plate boundary.
How wearing contact lenses all day can DESTROY your eyesight: Read one woman's cautionary tale. 1  Fashion designer Aimee McWilliams, 33, from London wore contacts daily. 2  Up to 8 hours wear a day is recommended but she wore them for 14.
How long do spark plugs last? Hovig Manouchekian, operations manager at Funk Brothers Automotive in Los Angeles, says there are two types of spark plugs: copper tip plugs, which last 30,000 miles, and platinum and iridium tip plugs, which have a life expectancy of about 100,000 miles.