How do you determine luster

The ability to resist being scratched—or hardness—is one of the most useful properties for identifying minerals. Hardness is determined by the ability of one mineral to scratch another. Federick Mohs, a German mineralogist, produced a hardness scale table 5 using a set of ten standard minerals.

The scale arranges the minerals in order of increasing hardness. Each higher-numbered harder mineral will scratch any mineral with a lower number softer. A rough measure of mineral hardness can be made by assembling a kit of handy objects table 6. A fingernail has a hardness ranging from 2 to 2. A mineral hardness test kit can be easily created from common household or hardware items table 6. Parents should help children make the kit. Wear safety glasses and gloves when cutting class.

All pieces in the hardness test kit should be compared to one another and specific minerals with a known hardness. Luster is how a mineral reflects light. Many minerals are colored by chemical impurities. Purple quartz, known as amethyst, and clear quartz are the same mineral despite the different colors. Streak is a more reliable property than color because streak does not vary.

Minerals that are the same color may have a different colored streak. Many minerals, such as the quartz in the Figure above , do not have streak. To check streak, scrape the mineral across an unglazed porcelain plate Figure below. Yellow-gold pyrite has a blackish streak, another indicator that pyrite is not gold, which has a golden yellow streak.

Mineralogists have special terms to describe luster. 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. Different types of non-metallic luster are described in Table below.

Can you match the minerals in Figure below with the correct luster from Table above? Hardness is a measure of whether a mineral will scratch or be scratched. Mohs Hardness Scale, shown in Table below, is a reference for mineral hardness. With a Mohs scale, anyone can test an unknown mineral for its hardness. Imagine you have an unknown mineral. There is no scientific method to determine luster. Often, determining the luster of a particular specimen is personal; to some it may appear as one type of luster, and to others as a different type.

It is in the eyes of the viewer to determine what luster a particular specimen exhibits. Luster is only a useful form of mineral identification when the specimen in question displays a unique luster, such as waxy, greasy, pearly, etc. Specimens with a vitreous luster cannot be distinguished from one another, nor can minerals with a metallic luster.

Luster is usually just noted as a mineral property, and is not commonly usually used to help identify a mineral. Observe the specimen in well lit conditions where its luster is visible. The surface being viewed should not be tarnished, unclean, discolored, or coated. Some minerals exhibit a pearly luster on cleaved surface s, so it is a good idea to check for luster on uncleaved portions of the crystal. Gold, 3cm tall, California. Euxenite, Wyoming, 2cm across. Diamond, Zaire 1 cm. Sphalerite, 4 cm across, Spain.

Pollucite 3cm. Stellerite, Pakistan, 2 cm across.