Mineral Identification Basics

1. Mineral Identification Basics PHYSICAL PROPERTIES COLOR Amethyst Ionic Iron Hematite Inclusions Chlorite inclusions Clear - Without Impurities Quartz comes in a wide range of colors. It is very easily colored by even trace amounts of impurities. (*) Various colors of Quartz.

2. Mineral Identification Basics INDICATIVE COLOR Azurite (*) Sulfur Malachite Turquoise Rhodochrosite Some minerals do have a certain color associated with them. Here are some examples: (*)

3. Mineral Identification Basics PHYSICAL PROPERTIES SPECIFIC GRAVITY The SPECIFIC GRAVITY of a mineral is a measure of the mineral’s density. It is related to the types of elements that make up the mineral and how they are packed into the mineral’s atomic structure. (*) Gold has a Specific Gravity of 19.2. It is 19.2 times the weight of an equal volume of water. Water has a Specific Gravity of 1. (*) Gold in Quartz

4. Mineral Identification Basics PHYSICAL PROPERTIES SPECIFIC GRAVITY The SPECIFIC GRAVITY of a mineral is determined by weighing the specimen in air and then weighing it in water. Here is the formula: (*) Weight in air Specific Gravity = (Weight in air) - (Weight in water ) (divided by) (*)

5. Mineral Identification Basics PHYSICAL PROPERTIES SPECIFIC GRAVITY Triple Beam Balance This is the equipment used in the lab at GCC to determine Specific Gravity. (*)

6. Mineral Identification Basics PHYSICAL PROPERTIES SPECIFIC GRAVITY The first thing to check in using the balance is to make sure it balances at the zero mark when the tray is empty. (*) This circle shows the zero mark and that the balance is calibrated correctly. (*)

7. Mineral Identification Basics PHYSICAL PROPERTIES SPECIFIC GRAVITY Notches (*) NO Notches (*) Notice that the top three bars of the balance have notches. These are the positions in which the weights are REQUIRED to rest. (*) Balance is in “Balance” (*)

8. Mineral Identification Basics PHYSICAL PROPERTIES SPECIFIC GRAVITY NO Notches (*) The bottom bar has no notch. Instead the weight (the small chrome sleeve sitting over the zero mark on the left) simply slides along this bar. It reads 0.1 to 0.01 grams. (*)

9. Mineral Identification Basics PHYSICAL PROPERTIES SPECIFIC GRAVITY Selecting the right material. (*) Opal in Rhyolite Not just any mineral will do. In determining the specific gravity of a mineral it must be pure, free of pockets or cracks (places that can trap air) and it should not easily dissolve in water. (*) Calcite with Garnet Sphalerite Limonite Halite

10. Mineral Identification Basics PHYSICAL PROPERTIES SPECIFIC GRAVITY The Limonite is full of pore spaces. It is almost like a sponge. When it is weighed in water it has numerous trapped air pockets that will make it lighter that it should be. (*) Opal in Rhyolite Calcite with Garnet Sphalerite Limonite Halite It would be difficult to get an accurate weight. (*)

11. Mineral Identification Basics PHYSICAL PROPERTIES SPECIFIC GRAVITY This is not a pure specimen. It is a combination of two minerals. The result of the specific gravity process would only give you an average of the two minerals. (*) Opal in Rhyolite Calcite with Garnet Sphalerite Limonite Halite

12. Mineral Identification Basics PHYSICAL PROPERTIES SPECIFIC GRAVITY The opal in rhyolite has the same problem as the calcite with garnet. It is not a pure sample (*) Opal in Rhyolite Calcite with Garnet Sphalerite Limonite Halite

13. Mineral Identification Basics PHYSICAL PROPERTIES SPECIFIC GRAVITY Halite is a salt. When weighed in water it dissolves. It would be difficult to get an accurate reading as it would become lighter and lighter as it slowly dissolved. (*) Opal in Rhyolite Calcite with Garnet Sphalerite Limonite Halite

14. Mineral Identification Basics PHYSICAL PROPERTIES SPECIFIC GRAVITY Sphalerite (pronounced: sfal er ite) is a good choice. It is a pure sample with no crack or pore spaces. And, it does not dissolve in water. (*) Opal in Rhyolite Calcite with Garnet Sphalerite Sphalerite Limonite Halite

15. Mineral Identification Basics PHYSICAL PROPERTIES SPECIFIC GRAVITY 100 grams is too much. Weight in air = 37.0 grams (*) Determine the weight of the Sphalerite (*)

16. Mineral Identification Basics PHYSICAL PROPERTIES SPECIFIC GRAVITY Weight in Water The weights are in the same place but now that the sphalerite is submerged in water it is lighter, and the balance is again out of balance. (*)

17. Mineral Identification Basics PHYSICAL PROPERTIES SPECIFIC GRAVITY Weight in Water It is important to note that the specimen being weighed is not resting on the bottom of the beaker or touching its sides. It is also completely submerged beneath the water. (*)

18. Mineral Identification Basics PHYSICAL PROPERTIES SPECIFIC GRAVITY 0 grams 20 grams 7 grams 0.94 grams Weight in Water (*) The weight of the sphalerite in water is 27.94 grams. (*)

19. Mineral Identification Basics PHYSICAL PROPERTIES SPECIFIC GRAVITY Weight in air Weight in air Specific Gravity = Specific Gravity = (Weight in air) - (Weight in water ) (Weight in air) - (Weight in water ) 37.00 grams 37.00 grams 27.94 grams Specific Gravity = 4.06 Note that there are no units. The grams cancel out. This is a ratio of how heavy the mineral is compared to an equal volume of water. The sphalerite is 4.06 times heavier than water. (*)

20. Mineral Identification Basics PHYSICAL PROPERTIES TASTE IT IS NOT RECOMMENDED THAT A TASTE TEST BE PERFORMED ON MINERALS AS A STANDARD PROCESS. SOME MINERALS ARE TOXIC. However, the mineral HALITE is common salt and has a unique taste. (*) Halite cubes from Trona, CA (*)

21. Mineral Identification Basics PHYSICAL PROPERTIES MAGNETISM MAGNETISMis the ability of a mineral to be attracted by a magnet. This most commonly is associated with minerals rich in iron, usually magnetite. (*) This is a piece of MAGNETITE with a magnet adhering to it. Magnetite is a mineral that is strongly magnetic in that a magnet will easily be attracted to it. (*)

22. Mineral Identification Basics PHYSICAL PROPERTIES MAGNETISM More sensitivity is achieved if instead of a large sample, small pieces are used. In this way, even weakly magnetic minerals will be attracted to the magnet. (*)

23. Mineral Identification Basics PHYSICAL PROPERTIES MAGNETISM This is a sample of “black sand” from Lynx Creek, Arizona. Its dark color is due to its high concentration of magnetite. See what happens when a magnet is place beneath the bottom right portion of the paper. (*) This technique is used to separate out much of the unwanted material in the search for gold in placer deposits. (*)

24. Mineral Identification Basics PHYSICAL PROPERTIES MAGNETISM LODESTONE is a variety of Magnetite that is naturally a magnet. (*)

25. Mineral Identification Basics DOUBLE REFRACTION DOUBLE REFRACTION:Isa property shared by many minerals ( but not those in the isometric crystal system). It is produced by the separating of a beam of light as it passes through the crystal structure. It is best displayed in the mineral CALCITE. This image clearly shows the double image below the calcite. (*)

26. Mineral Identification Basics CHEMICAL PROPERTIES REACTION TO HYDROCHLORIC ACID Some minerals, notably the carbonates, react to cold dilute HCl. In this illustration a piece of CALCITE is shown to react (fizz) after HCl is applied. (*) Calcite Reacts to HCl (*)