In 2002, NASA’s THEMIS spacecraft began orbiting Mars, scanning the surface of the planet with a thermal emission imaging system. Instruments on the spacecraft had the ability to characterize the mineralogy of rock units exposed on the surface of Mars. Their goals were to identify the rock types on the surface of Mars and map their geographic…

Many specimens of dacite are fine-grained and of relatively uniform composition. Ancient people have knapped them into sharp tools and worked them into utilitarian objects. When knapped into projectile points, scrapers, and knife blades, they have an edge that is not as sharp as obsidian but is much more durable.

Dacite is sometimes used to produce crushed stone. It performs well as fill and as a loose aggregate in a wide variety of construction projects. It does not perform well as a concrete aggregate because its high silica content reacts with the cement.

Dacite magma generally develops in subduction zones were a relatively young oceanic plate is subducting under a continental plate. As the oceanic plate descends into the mantle, it undergoes partial melting with liberated water facilitating the melting of surrounding rocks. The subduction zone where the Juan de Fuca plate subducts under the North America plate…

A generalized mineral composition for dacite is intermediate between rhyolite and andesite. It usually contains more quartz than andesite and more plagioclase than rhyolite. The plagioclase feldspars are often oligoclase, andesine or labradorite. Dacite can be considered the fine-grained equivalent of granodiorite. Plagioclase is the most abundant mineral in many dacites. Other minerals that might be found in dacite include quartz, biotite, hornblende, augite, and enstatite. Dacites consisting mostly of…

Dacite is a fine-grained igneous rock that is normally light in color. It is often porphyritic. Dacite is found in lava flows, lava domes, dikes, sills, and pyroclastic debris. It is a rock type usually found on continental crust above subduction zones, where a relatively young oceanic plate has melted below.