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.
Cost of Contact Lens Solutions. Don't forget about the cost of contact lens solutions to clean and disinfect your lenses. If you wear contacts on a daily wear basis and clean and disinfect them after each use, expect your annual cost for contact lens care solutions to be roughly $150 to $200.So to determine your combined yearly contact lens costs for lenses and solutions, add $150 to $200 to the above totals.f you replace your contacts approximately every two weeks, this means you need about five boxes (30 lenses) per eye, or a total of 10 boxes per year. This comes to an annual contact lens cost of roughly $220 to $260 (lenses only).