Many minerals produce a white streak, and some geologists prefer using a black streak plate for these minerals because the mineral particles in the streak are easier to observe.

Usually there are two colors, often black and white, or green and white, of black and tan or pink. Ribbon like layers are found in the rock, gneiss. In schists, the layers are most often thin layers of mica or chlorite around lens shaped masses of feldspar or quartz.

The surface across which the mineral is dragged is called a “streak plate”, and is generally made of unglazed porcelain tile. In the absence of a streak plate, the unglazed underside of a porcelain bowl or vase or the back of a glazed tile will work.

These white, 1 x 2 inch unglazed porcelain tiles are ideal for streak testing minerals. The streak test is essential in mineral identification because it retains the color of the mineral.

One simple way to classify luster is based on whether the mineral is metallic or non-metallic. Minerals that are opaque and shiny, such as pyrite, have a metallic luster. Minerals such as quartz have a non-metallic luster. Luster is how the surface of a mineral reflects light.

Follow this easy, step-by-step activity:

1. Hardness test — Scratch the rock with a fingernail, a copper penny, a glass plate or nail, and a ceramic plate.
2. Color streak test — Test for the “color streak” of the minerals by rubbing the rock across the ceramic plate in the Mineral Test Kit, or across smooth.

Most geodes contain clear quartz crystals, while others have purple amethyst crystals. Still others can have agate, chalcedony, or jasper banding or crystals such as calcite, dolomite, celestite, etc.

Geodes are the minerals that have other minerals inside of their cavity. The geode structure is one of the most striking crystalline structures you can find in the gemstone world. These are often created with Chalcedony Quartz found internally within a rock. That is what makes this such a stunning stone.

A nodule is something roughly spherical deposited in a matrix. When the nodule has a cavity it is a geode. Often Chalcedony will deposit as a nodule or a geode. When the Chalcedony is banded it is an agate, although some chalcedonies that aren’t banded are still called agate, like moss agate, fire agate, etc.