Montana Moss Agate

My pet rock is (as you may have guessed) is agate, or to be more specific, Montana moss agate. It is transparent and amber colored with spots of darker material inside it and whiter edges. Around the edges are small rocks that have been slowly cemented to it. The rock is actually a cross-section of a larger piece of agate, which was a rounded rectangular shape. The outside edge is rough, being composed mainly of small rocks, but the sides are smooth, cut by a rock saw. The luster is a dull pearly one, but if held up to the light, this agate changes its appearance completely.

This rock is an extrusive igneous rock, which was probably formed in the area of Yellowstone National Park that coincides with Montana when huge lava flows swept over the forest, burning down large forests which would in turn grow again only to be leveled by more lava flows. Pieces of these trees were trapped in the quartz-rich lava as it hardened. After hundreds of years of these landflows, silica-filled rain began to fall, filling the pockets in the lava left by the trees with silica and forming the dark spots in the agate. Over time this agate was weathered into small pieces.

The two main minerals in this agate are quartz and silica, though there are small amounts of other minerals and elements. Its relative rock is chalcedony.

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