Slate occurs in nature, with numerous minerals contributing to its various characteristics. In the Slate Valley of Vermont and New York there is a strong prevalence of chromates, which color the slate green. This slate has two forms: ‘Unfading Green’ and ‘Weathering Green’.
The characteristic of Unfading Green slate is that the color remains the same, no matter how much time it is exposed to the elements. It is a darker, more luminous green. Weathering green slate, also referred to as Sea-green, however, reacts with sunlight and a good portion of it ‘weathers’ to peach, tan, yellow and buff colors, due to the presence of iron oxides. A prevalent oxide is Limonite, which is yellow (like a lemon). Weathering does not make it an inferior slate. In fact it usually outlasts its unfading counterpart.
Mixing these slate together, with additional highlights of purple slate make up the traditional Vermont Blend, used frequently throughout the United States.