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Mineral name: Quartz

Chemical formula: SiO2

Physical properties: vitreous luster, hardness 7, no streak, conchoidal fracture, hexagonal crystals

Light and Dark Minerals

In the Minerals unit, we learned that color is not usually reliable for identifying minerals. While it is not a good way to identify minerals, thanks to the melting points of different minerals, it can be useful for identifying igneous rocks.

Remember that igneous rocks form from magma, and not all magmas are the same. Some are hotter (more than 1300°C/2400°F), and some are cooler (as low as 700°C/1300°F). Because different minerals melt at different temperatures, hot magmas are usually very different chemically from cooler magmas.


Mineral name: Gypsum

Chemical formula: CaSO4·2H2O

Physical properties: vitreous luster, hardness 2, white streak, Two directions of cleavage

Geology in the City

What if you live in a big city, with no road cuts or rock outcrops nearby? Are you out of luck for finding rocks to study? No! Many of the buildings in most cities have decorative stonework covering their outer walls and their lobbies. You won't be able to collect specimens, but you can collect some marvelous photographs.

Feldspar Group

Mineral name: Feldspars are a group of minerals made of aluminum, silicon, and oxygen. Examples include orthoclase, plagioclase, labradorite, and microcline.

Chemical formula: KAlSi3O8 – NaAlSi3O8 – CaAl2Si2O8


Quartz crystal

The beauty and precision of crystals leads many people to collect minerals. They look more like cut gemstones than something that was dug up out of the ground. Each mineral has one or more crystal forms, and those forms can be used to help identify the mineral.

Crystals form in different ways, and we will explore them by growing some crystals of our own.