Opal-AN

specimen number:
2354027

location:
White Oak, Montgomery Co., Maryland, USA

description:
Attractive blue bubbly botryoidal crystalline opal-AN across the top of a granite matrix.

In the White Oak area of Montgomery County, Maryland, the regional geology is dominated by the metamorphic crystalline rocks of the Piedmont Province, including weathered granitic and gneissic formations. Amorphous silica-rich solutions circulating through fractures and cavities in these rocks led to the secondary deposition of non-precious opal, primarily occurring as the clear, glass-like variety known as hyalite or amorphous network silica. While the region was never a major site for commercial opal mining, the area gained interest among mineral collectors in the mid-to-late twentieth century, particularly during local construction projects, road excavations, and rock outcrops that briefly exposed collector-quality, botryoidal coatings and crusts of hyalite opal on host rock.

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