In this issue:
How To Crack a Geode
A geode looks like an ordinary igneous or sedimentary rock, but the inside is often full of crystals! You can find geodes "in the wild" in some parts of the country, or at rock shops or science supply stores.
>> Watch our project video to see us crack open some geodes and find crystals inside!
Geodes are formed when there is a hollow cavity in solid rock. This cavity can form in several ways: by a gas bubble in a lava flow, by limestone being dissolved by an acidic substance, or by a shell not being filled completely with sediment when it is fossilized. When mineral-rich ground water gets into these cavities, the minerals can form crystals, depending on the temperature, pressure, and the amount of water. (Go here to learn more about crystals.)
Each geode is unique. Some will have large colorful crystal formations, others may have solid bands of quartz, and still others will have mineral deposits but no crystals formed yet. Sometimes a geode might be full of silt or sediment. This kind is called a "mud ball." If you are selecting your own geodes, try to choose ones that seem light for their size; these are more likely to be hollow in the center and have crystal formations.
For a fun activity you can do with household materials, check out our Make Your Own Geode project!
Rocks & Minerals Project Kit
This science kit makes an excellent introduction to the world of rocks and minerals! The projects in this set provide hands-on fun for kids of all ages, as they get to identify 30 unique specimens, plus crack open a geode, grow crystals on a rock, make their own sedimentary rock, and much more. The instruction manual includes information on the rock cycle, crystal formations, and geodes.
If you've ever been to the beach, you've probably picked up rocks that are perfectly smooth and rounded. The ocean is a natural rock tumbler: as rocks are rolled by the waves and rubbed against sand and each other, their rough edges and corners are filed away. A rock tumbler can mimic this process and even take it a step further by adding polish to make the stones shine. Rock tumblers work much faster (4-6 weeks) than the ocean because their motion is constant and they use an abrasive substance called silicon carbide, which is much harder than sand.
Lapidary is the art of cutting and polishing gemstones. Rocks and minerals come in all different colors and patterns, and polishing them to a smooth shininess brings out their incredible beauty. Polished rocks are often used in jewelry.
When selecting rocks to polish in a tumbler, there are several things to consider:
Your rock tumbler will come with full instructions, but here are the basic steps to polishing a set of rocks:
A gem or a gemstone is any mineral that can be cut and polished for jewelry or other decoration. The most precious gems are chosen for their beauty, rarity, and durability. Semi-precious gems usually have one or two of these characteristics, but fall short in some area. Fluorite, for instance, is very beautiful but it is too soft and will scratch easily. Agate, quartz, and amethyst are other examples of semi-precious gems.
Diamonds are gemstones that are considered very precious, and for good reason. Though they are made of carbon, one of the most common elements, diamonds are generally regarded as some of the most beautiful gemstones. They are relatively rare, because much diamond is not of jewelry quality. Diamond mines usually have 1 part diamond to 40 million parts other rock, but a diamond high-quality enough to be in an engagement ring is the product of the removal and processing of 200 to 400 million times its volume of rock! The diamond's strongest point, however, is its durability. It is the hardest substance found in nature, four times harder than the next hardest natural substance, corundum (sapphire and ruby). The grit in a regular rock tumbler wouldn't have much effect on a diamond! It also has the highest melting point, and conducts heat five times better than the second best element, silver.
More Rocks & Minerals:
Check out this gemstone gallery to see how beautiful rocks can be!
Watch these amazing animations to see crystals grow!
Get some tips for how to make tumbled rock jewelry.