Examples of igneous rocks are pumice, obsidian, basalt, and rhyolite.
Obsidian is black glass formed by volcanoes.
because an obsidian rock has low silica
Igneous rocks
Obsidian
Vinegar, which is acidic, reacts with the calcite or limestone present in sedimentary rocks, resulting in the release of carbon dioxide gas. The fizzing or bubbling you observe is the visible evidence of this reaction. This reaction between the acid and the calcium carbonate in the rock is similar to the reaction that occurs when acid is added to baking soda.
Glassy rocks are rocks that have cooled and solidified quickly, without forming crystals. This rapid cooling prevents mineral crystals from growing, resulting in a smooth and glass-like texture. Obsidian and pumice are examples of glassy rocks.
Very smooth rocks are called "polished rocks" or "river rocks" due to the smooth texture achieved from erosion in water bodies like rivers and oceans.
A while.
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obsidian
One word for this is obsidian. Obsidian is a gorgeous hard stone, usually but not always black, and sometimes with iridescent, almost opalescent highlights. Tachylite is also a volcanic glass of basaltic composition.