minerals

Growing Crystals from Solution

One way that crystals form is from chemicals dissolved in water. If the water gets cooler, dissolves other chemicals, or evaporates, some of the dissolved chemicals can be deposited as crystals. Often, growing crystals can be a fairly long, involved process, but with this activity, we will grow some nice crystals quickly and easily.

To try this, you will need:

What is a Rock?

The word rock means different things to different people. As with many words, its scientific meaning is different from many of the meanings used in everyday language, so lets start with a short video on the scientific definition of a rock.

Minerals: Streak

To perform the streak test, you rub a specimen on a piece of unglazed porcelain tile. Go to your local hardware store, and look at the backs of their floor tiles. You want a tile that is made of porcelain, and the unglazed back should have a white color.

These tiles are very hard (hardness 6.5), and they have a rough surface. As you rub the mineral across that surface, it acts like a file, powdering up some of the mineral. The color of that powdered mineral is its streak color.

Identifying Minerals


A few common minerals.

With nearly 3000 different known minerals, you might think that identifying mineral specimens would be difficult. Actually, it is usually fairly easy. Many of those 3000 minerals are very rare, only found in very limited areas. If you can learn to identify twenty or thirty of the most common minerals, you will be able to identify most of the specimens that you are likely to find.

Minerals: Luster

At first, many people find luster a bit confusing. Luster is the way that an object reflects light, and although the different types of luster can be difficult to describe, your daily experience makes them easy to recognize. Once you understand luster, you will recognize the common lusters instantly.

Hydrothermal Quartz

Hydrothermal veins are a combination of the two ways that crystals form. Magma contains water as well as molten rock. Because it is underground, and under tremendous pressure, the water stays a liquid. At very high temperatures and pressure, that water can dissolve quite a few minerals. As the magma cools, the last part that is still a liquid is the quartz and the high temperature/high pressure water. They flow into cracks in the surrounding rocks, where they cool. The quartz starts to solidify quickly, but the hot water keeps some of it dissolved.

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