My biggest largest opal I have encased, 17 grams. The marble is roughly 2 inches and diameter with a massive opal white opal. This is a synthetic opal and are made from 100% silica. Always push them limits of what's possible | Sno Glass

Sue from @brokenrivermining presents: Opal Fossils with Unpreserved Internal Details Opal formation commences when silica dissolves in water. At our Russell’s opal mine we have found that this silica solution occupies a void most probably left by decaying tree roots or branches. When it solidifies it creates an opalized replica of the original object. These are also known as ‘jelly mould’ fossils. In some rare cases, like shown above, we have found large and rare opal fossil specimens with beaut