Sometimes there are bits of basalt too. These bits of rock are called cinders. They may be tiny, like ash, or larger like gravel. They get blown out of the vent and harden in the air. When they land, they pile up around the crater to form a steep cone.
Cinder cones are often smaller than shield volcanoes, and they wear away easily.
The layers of cinders makes the sides steep, and the layers of hardened lava keep them from wearing away fast. Many famous volcanoes like Mt. Saint Helens and Mt. Rainier in Washington are stratovolcanoes. Mt. Rainier, Washington Caldera volcanoes are very large stratovolcanoes that collapsed after an eruption. Crater Lake in Oregon is an example of a caldera. About 7000 years ago it was a volcano we now call Mt. Mazama.