This Fairy Stone is from Lake Placid, New York. This piece measures approx. 61 x 23 mm: thickness is approx. 9 mm: weight is 20 grams.
 
Fairy Stones are a mixture of Calcium Carbonate and Clay. They tend to form in disc shape. They are also known as Melinite Opal or Goddess Stone. They have a MOHS of 5 and can be found in US, Canada, Greenland, UK and Morocco.