Day 6: Mineral Properties (Pgs 9-11)
In today's lesson, we discuss what we learned about physical properties in our Chemistry 1 unit: Chemical & Physical Properties, and discussed how we use physical properties to identify substances. Minerals are a particular type of substances. We can use some of the identifying properties of physical properties to identify minerals. Today, we only focused on 5 major physical properties of mineral substances:
Hardness is set on a scale of 1-10. 1 being the softest (talc) and 10 being the hardest (diamond). The scale includes 10 common minerals that are set as the standard for hardness.
When you scratch two minerals together, one will leave a groove (scratch), the other will leave residue (streak). The one that leaves a streak is soft, the one that leaves the scratch mark is harder. So, if I were to scrape diamond to quartz, quartz will have a scratch mark on it from the diamond, and quartz will leave a residue or streak on the diamond.
We use this scale to determine the minerals hardness. The series of tests to determine the hardness begins with the softer ones first, then you work your way up to the harder ones until the mineral that you are testing gets scratched. Once it gets scratched - the number that determines the relative hardness is a little less than the one that scratched it, and a little higher than what it scratched.
For instance, Pyrite, or fools gold, is 6.6 on the hardness scale (Pocket Ref, Glover, 2005). As I move up the scale, the pyrite will scratch all the minerals from Talc through Orthoclase; however, it will not scratch quartz. Therefore, the hardness number must be somewhere between 6 & 7. For our purposes in this lab, a hardness number set at 6.5 is sufficient.
In this lab, I will not provide you with hardness numbers, but I will provide you with information about a virtual scratch test based on the information I have about that mineral. Your job will be to determine its hardness on a scale of 1-10.
Other properties are also listed, but I do not "give" you the answer - rather, I give you hints, with the exception of streak. Use your observational skills to determine the other properties and list them in your book.
Mineral Properties Lab:
Below are some pictures and some basic properties of the minerals listed in your lab book on page 10. To enlarge the images, simply click on it.
- Luster: How light reflects, refracts, or absorbs light. Some descriptive words include: metallic, glassy, brilliant (like a diamond), dull, earthy, waxy.
- Color: need I say more?
- Streak: the powdery version of the mineral when scraped across a streak plate. This is the true color of the mineral. To describe the streak, simply describe the color.
- Special properties: some minerals can be identified by special properties like magnetic, or they light up under florescent light. This property is the one true identifier that separates it from the rest of the pack.
- Hardness: Hardness is determined by the strength of the bonds between the molecules that make up the mineral. Hardness is relative to each other and is determined by scratching one on the surface of the other and looking for a scratch mark or a streak mark. Look at the diagram below.
Hardness is set on a scale of 1-10. 1 being the softest (talc) and 10 being the hardest (diamond). The scale includes 10 common minerals that are set as the standard for hardness.
- Talc - Softest
- Gypsum
- Calcite - soft
- Fluorite
- Apatite - Medium
- Orthoclase
- Quartz
- Topaz - Hard
- Corundum
- Diamond - Hardest
When you scratch two minerals together, one will leave a groove (scratch), the other will leave residue (streak). The one that leaves a streak is soft, the one that leaves the scratch mark is harder. So, if I were to scrape diamond to quartz, quartz will have a scratch mark on it from the diamond, and quartz will leave a residue or streak on the diamond.
We use this scale to determine the minerals hardness. The series of tests to determine the hardness begins with the softer ones first, then you work your way up to the harder ones until the mineral that you are testing gets scratched. Once it gets scratched - the number that determines the relative hardness is a little less than the one that scratched it, and a little higher than what it scratched.
For instance, Pyrite, or fools gold, is 6.6 on the hardness scale (Pocket Ref, Glover, 2005). As I move up the scale, the pyrite will scratch all the minerals from Talc through Orthoclase; however, it will not scratch quartz. Therefore, the hardness number must be somewhere between 6 & 7. For our purposes in this lab, a hardness number set at 6.5 is sufficient.
In this lab, I will not provide you with hardness numbers, but I will provide you with information about a virtual scratch test based on the information I have about that mineral. Your job will be to determine its hardness on a scale of 1-10.
Other properties are also listed, but I do not "give" you the answer - rather, I give you hints, with the exception of streak. Use your observational skills to determine the other properties and list them in your book.
Mineral Properties Lab:
Below are some pictures and some basic properties of the minerals listed in your lab book on page 10. To enlarge the images, simply click on it.