![](https://www.windows2universe.org/earth/geology/images/3quartz_sm.JPG)
These three crystals of the mineral quartz show how the same type of mineral can have different colors! Windows to the Universe | ![](https://www.windows2universe.org/earth/geology/images/amathyst_sm.jpg)
Amethyst crystals from Brazil Courtesy of Corel Photography |
![](https://www.windows2universe.org/earth/geology/images/AGI_brach1_sm.jpg)
A fossil brachiopod! Oklahoma University/Earth SceinceWorld Imagebank | ![](https://www.windows2universe.org/earth/geology/images/calcite_sm.jpg)
This photograph shows several crystals of the mineral, calcite. The crystals in this example are shaped like pyramids. Therefore, the crystals are known as "dogtooth". Courtesy of Corel Photography |
![](https://www.windows2universe.org/earth/geology/images/feldspar2_med.jpg)
Orthoclase feldspar Windows to the Universe Image | ![](https://www.windows2universe.org/earth/geology/images/gypsum2_med.JPG)
Gypsum Windows to the Universe/L.Gardiner |
![](https://www.windows2universe.org/earth/geology/images/hematite_med.jpg)
This is a photograph of the mineral, hematite. Hematite contains lots of iron. The chemical formula for hematite is Fe2O3. Windows to the Universe original image | ![](https://www.windows2universe.org/earth/geology/images/pyrite_sm.jpg)
Crystals of the mineral Pyrite from Peru Courtesy of Corel |
![](https://www.windows2universe.org/earth/geology/images/quartz_crystals_med.JPG)
These two examples show the shape of individual quartz crystals. Windows to the Universe Image |