Quartz occurs as clear or cloudy crystals in a range of colors. It's also found as massive veins in igneous and metamorphic rocks. Quartz is the standard mineral for hardness 7 in the Mohs hardness scale.
This double-ended crystal is known as a Herkimer diamond, after its occurrence in a limestone in Herkimer County, New York. That's where I dug up this specimen. Once you're familiar with quartz, it's easy to recognize in many different settings.