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.
In Europe and Asia, Daily Disposables are one of, if not the leading modality for contact lens wear, but in the US, daily disposables have captured only about 5% of the contact lens market. The primary reason is cost-to wear daily-disposable contact lenses full-time, you need about 360 pairs a year.oreover, daily-disposable contacts are generally considered the safest and healthiest type of contact lenses because the use of a fresh pair of lenses every day minimizes the chance for build-up of harmful pathogens on the lens surface. Each of the major US contact lens manufacturers offers a daily disposable contact.