 lecture coincides with an online textbook at opengeology.org made by solid community college faculty including myself. And today we're going to learn about identifying minerals and how geologists do it. This is for introductory level material. So identifying minerals is relatively easy. As discussed in one of the previous lectures there are well over 4,000 different minerals out there and with a little bit of observation and a few simple tests you can narrow down a lot of those minerals to just a just a handful of potential candidates. One thing to keep in mind is that the most part there's a lot of extremely common there's just a handful of extremely common minerals out there. So I think I had to memorize a little bit more than 100 for my mineralogy class. It was a class devoted to studying minerals. There's a few physical properties that that some minerals can tell you that are dead giveaways for that mineral. So first let's talk about color and translucence. A lot of times color is not a great indicator of the type of mineral that you're looking at. Take for example these different specimens of fluorite. In the bottom corner here you have yellow and translucent and green and beautiful signature purple fluorite. Same goes for quartz. In fact there's whole slew of colloquial type names for different color variations of quartz. So however the amount of translucence how easily light passes to that mineral can sometimes be indicative of the type of mineral that you're looking at. And here's some of the words that we use opaque meaning you can't see through it. Translucent meaning it allows some light to go through it and of course transparent like a sheet of glass you can see through it completely. Luster is a little bit better of an indicator of the type of mineral that you're dealing with. And the first kind of major split that we do is metallic versus non-metallic. Does it look like a piece of metal? If so we call that a metallic luster. And if it doesn't look metal and I'm not saying shiny because there's lots of non-metallic lusters that are shiny but if it does not look like metal then we call that non-metallic. Here's a beautiful example of some quartz and you can see there's a lot of glassy looking lusters happening in this specimen. So you can also have like an earthy luster or pearly luster, silky luster, greasy luster. They're all kind of intuitive names for how the appearance of the piece, how it's reflecting light, not so much as the color but the general texture appearance. Here's some examples. This galena cube here looks like a piece of metal. I would call that a metallic luster. Here's where you kind of get into a gray area because this does look like rusty metal. We call this a sub-metallic or earthy luster. Followed into the non-metallic category and a few of most geologists. Streak is a little bit more indicative of minerals. True color, it's basically the powdered color of the color of the powdered mineral. You get these ceramic plates which are fairly hard and we'll talk about hardness in a second and you try to powder the mineral on the plates and you see what kind of color you get. Most of the traditional streak plates are white and here's a piece of pyrite streaked across this white streak plate. You see it's kind of a greenish black color. Not every mineral will make a streak on a streak plate and that's because of hardness. Sometimes a mineral cannot be broken down by the streak plate because it's harder than a streak plate. Sometimes if you can find crystals in the mineral you can use crystal shape as an indicator of the type of mineral you're dealing with. There's a fibrous crystal shape, cubic crystal shape, betrothal crystal shape which is kind of this bulbous hexagonal. Here's the classical hexagonal crystal shape of a quartz crystal here. Here's some fluorite. Of course keep in mind that there's a lot of minerals that share the same type of crystal shapes. If you're willing to destroy your sample you can test its strength and tenacity, how easily it breaks apart into smaller bits. The tenacity is its resistance to breaking or deforming. It's malleable. You can form it and flatten it very easily like gold. Here is a very common test we use for identifying minerals and this is known as hardness. This is how easily the mineral can scratch. Diamond is known for its hardness. It's one of the hardest minerals known to mineralogists with the exception of a couple of minerals we found in much smaller quantities than diamond. There are a couple of naturally occurring minerals that are a little bit harder than diamond. They only occur in very many quantities. The higher the number that we designate for the hardness, the harder the mineral and a harder mineral will scratch a softer mineral. So something with the ten is almost impossible to scratch. A fingernail falls about a 2.5 on hardness scale and glass is about a five and a half on the hardness scale. Those are usually the two things I use to kind of bracket in the hardness of the mineral I'm working with. Here's the Mohs hardness scale and here's different kind of minerals used to designate the different numbers on the hardness scale. Taupe, gypsum, calcite, fluorite, apatite, orthoclase, quartz, topaz, corundum, and diamond going from one to ten. It's kind of an arbitrary scale but it allows us to figure out the hardness of different minerals that we're looking at and helps this idea. Notice that quartz is higher on the hardness scale than glass and it's higher than fingernail. So if you can scratch a mineral with your fingernail, you know that the mineral is softer than your fingernail, softer than 2.5. Keep in mind that fake fingernails are a little bit harder than real fingernails. Cleavage is another really good indicator of what type of mineral you're dealing with and cleavage is essentially how the planes of weakness that the mineral will break along. So if you were to hit that mineral with a hammer, break it into tiny little pieces, it broke along certain planes, nice flat smooth sides. Those are your planes of weakness and you can be very descriptive with those planes of weakness, how many there are, in what directions and at what angles do those different planes meet and that can help you identify that. Here is an example of a mineral with one cleavage plane. This is biotite. Notice that it is breaking into thin sheets and that is a classic one plane of cleavage mineral. Here's a couple of different minerals with more planes of cleavage. Loretta I believe has four planes of cleavage. Calcite has three and they're not at 90 degrees so it forms like a rhombohedron, a tilted box shape. But notice when this mineral is broken, it broke into smaller pieces that are the same shape, really good indicator of cleavage. So the things I look for for cleavage in a mineral is broken off pieces that are the same angles and shapes as the main surfaces that I'm seeing. And that's a good indicator that you're dealing with cleavage planes. You can also, the mineral is semi-translucent or transparent, you can look for where those planes kind of cut across the mineral. Fracture, if cleavage is absent, is also a good indicator to help you identify a mineral. And quartz is ideal for identifying fracture. Concoital fracture is kind of like that chipped glass appearance that you see when a rock hits something. Here is an example of concoital fracture. Here's some irregular fracture is observed in quartz. This is a piece of obsidian but you can also see this kind of concoital chipped glass appearance in quartz. Specific gravity can also be a good indicator of a mineral. And galena is an especially good example of something of the high specific graph. Anything containing iron or lead, as galena contains lead, and it's heavier than it looks. And that's a good indicator that has the high specific gravity. Some other properties worth noting that some of the more common minerals have, halite, if you're willing to lick it, is salty to taste. And there's a beautiful picture of halite showing it's four planes of cleavage at 90, or three planes of cleavage at 90 degrees. Talc feels like talcum powder, soapy feel. Graphite has a greasy feel you can write on paper with it. Some minerals are magnetic like magnetite, creative name for magnetic mineral, hematite, both iron bearing minerals. Calcite can have a double refraction sometimes when it's especially translucent, but a more signature property of calcite is that it fizzes with dilute hydrochloric acid. So if you drop a couple drops of hydrochloric acid on it, it'll fizz profusely. That's a really good way to identify it. So that's it for identifying minerals. I hope you learned something.