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Difference Between Rocks and Minerals

Discover the distinction between rocks and minerals, the characteristics that define minerals, and how they form. Learn to identify minerals based on physical properties such as color, luster, streak, hardness, and crystal form.

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Difference Between Rocks and Minerals

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  1. Minerals

  2. What is the difference between rocks and minerals?

  3. Minerals are the ingredients of rocks. Or • Rocks are made up of minerals.

  4. What is a Mineral? • A mineral is a naturallyoccurring, inorganic, solid that has a crystal structure and a definite chemical composition. Pyromorphite

  5. Do you consider water a mineral? • Water is not a mineral since it is not solid and crystalline. • HOW ABOUT TUBE ICE? • Tube ice is not because it is not naturally occurring.

  6. What do all minerals have in common? For a substance to be a mineral it must have these 5 characteristics: 1. Formed by natural processes on or inside Earth- no help from humans 2. Is inorganic- was never alive. For example, although coal was formed naturally in earth’s crust it came from plants and is therefore, not a mineral

  7. What do all minerals have in common? For a substance to be a mineral it must have these 5 characteristics: 3. Is a solid, with definite volume and shape. Liquids cannot be minerals! 4. Minerals always contains certain elements that give it a unique chemical composition (makeup). Some minerals are compounds which are made up of more than one element.

  8. Definite chemical composition Definite chemical composition means that a mineral always contains certain elements in definite, or exact, proportions Almost all minerals are compounds in which two or more elements are combined so they no longer have their distinct properties. Some elements occur in a pure form in nature and are considered minerals (almost all are metals such as copper, silver, and gold)

  9. The Structure of Minerals • 5. Have a crystalline shape- the particles of a mineral line up in a pattern that repeats forming a crystal. • Crystal- solid with atoms arranged in an orderly, repeating pattern

  10. Crystal structure Top left from http://www.tuspirits.com/images/ArkansasCrystal867.jpg Top Right http://judie.co.nz/wp-content/uploads/2010/02/quartz_crystal_cluster_black.jpg Bottom Left http://www.mindat.org/photos/0554307001221343359.jpg Bottom Right http://t1.gstatic.com/images?q=tbn:ANd9GcSML6stZDnpe1vLvdPfB 3uOjrscEi3qsGmQpQ4LGwERlyB-Iww&t=1&usg=__7mdDC9sp-_A5hsegmp5Tp6eDizY=

  11. Which 2 of the following are not minerals? Why? • Talc • Flourite • Galena • Crude Oil • Quartz • Pyrite • Coal

  12. Which 2 of the following are not minerals? Why? • Talc • Flourite • Galena • Crude Oil- liquid (not solid) and organic (made of plant and animal remains) • Quartz • Pyrite • Coal- Organic (made of plant and animal remains)

  13. How do minerals form? There are 2 ways that crystals form: The cooling of hot, liquid rock called magma causes compounds to combine Magma cools slowly= crystals are large Magma cools quickly= crystals are small The evaporation of water that has minerals dissolved in it.

  14. How do we identify Minerals? • We look at Physical Properties • These include: • Color/Appearance • Luster • Streak • Hardness • Cleavage/Fracture • Crystal form • Specific gravity

  15. Physical Properties of Minerals(can be used to identify the mineral) 1.Color Can be misleading Many minerals will have a similar appearance, but will have different impurities Color and appearance are not enough to distinguish minerals

  16. color • Some minerals show a wide variety of colors • Quartz can be transparent, white, pink, brown, purple, yellow, orange and even black • Many minerals show very similar colors • Calcite, gypsum, barytes, fluorite, plagioclase feldspar and halite are commonly grey or white in color

  17. Color Examples of color variation in Fluorite

  18. Color Plagioclase feldspar Quartz Calcite Barytes Fluorite Gypsum All these minerals are grey or white in color

  19. Physical Properties of Minerals(can be used to identify the mineral) 2. Luster Luster refers to the way a mineral reflects light from its surface Metallic = shiny like metal Non-metallic = dull, non-shiny surface, can include pearly, silky, and glassy We can also use other terms such as waxy, pearly, glassy, dull, and silky Calcite has a non-metallic luster Pyrite has a metallic luster

  20. Metallic Luster Malachite Galena Minerals reflect light like metals. Metallic luster often tarnishes to a dull luster

  21. Pearly Luster Biotite Mica The luster of a pearl or mother of pearl Shows clearly on the cleavage surfaces of biotite and muscovite mica Also shown by Talc and selenite (a variety of gypsum) Muscovite Mica

  22. Silky Luster The luster of silk Occurs in minerals with a fibrous structure Satin spar (a fibrous form of gypsum) shows this to good effect 1cm Gypsum (Satin Spar)

  23. Resinous Luster The luster of resin The mineral has a grainy appearance Sphalerite, opal and amber show resinous luster 1cm Sphalerite (Zinc Blende)

  24. Adamantine Luster 5mm The luster of a diamond

  25. Dull or Earthy Lustre The mineral does not reflect light and has the same appearance as soil. Minerals such as galena have metallic lusters on freshly broken surfaces but they tarnish to dull with prolonged exposure to the atmosphere. 1cm Limonite has a dull or earthy lustre

  26. Luster • Luster describes how a mineral reflects light from its surface. Such as: • DescriptionExamples • Glassy Quartz • Silky Gypsum • Greasy Talc, some Quartz • Metallic Gold, Pyrite, Galena etc • Earthy Kaolin • Waxy some Serpentine • Pearly Gypsum, some Talc • Resinous Amber • Brilliant Diamond • Dull Graphite

  27. 3.Streak The color of the powdered form of the mineral We find a minerals streak by rubbing it on a white ceramic plate/streak plate The color of the streak can be different than the mineral Minerals must be softer than the streak plate Physical Properties of Minerals(can be used to identify the mineral)

  28. Streak • Obtained by rubbing a mineral specimen on an unglazed white porcelain tile • Useful for identifying metallic ore minerals • Silicates generally do not mark the tile and have no streak • White minerals streakedon a white tile will have a white streak • Any minerals harder than the tile (6) will scratch it Haematite gives a cherry red streak

  29. Streak…can help identify quartz BUT... http://www.childrensmuseum.org/geomysteries/cube/b3.html

  30. Streak 2 Malachite – pale green Haematite – cherry red Iron Pyrite – greenish black Galena – lead grey Sphalerite – pale brown Limonite – yellowish brown

  31. Metallic Ore Minerals – Characteristic Streaks

  32. 4.Hardness How easily a mineral scratches materials Physical Properties of Minerals(can be used to identify the mineral) • it is a measure of the resistance of a mineral (not specifically surface) to abrasion • The ability of a mineral to resist being scratched. • “Scratch test” • If mineral A can scratch mineral B, what does that tell us about the relative hardness of each mineral?

  33. Learning check! • If mineral Acan scratch mineral B, what does it tell us about the relative hardness of each mineral?

  34. Mohs Hardness Scale Scale from 1 (softest) to 10 (hardest) Test by seeing if the mineral can scratch different objects (like human fingernail, copper, penny, glass, steel file)

  35. Moh’s Scale of Hardness 10. Diamond 9. Corundum 8. Topaz 7. Quartz 6. Orthoclase Feldspar

  36. Moh’s Scale of Hardness 5. Apatite 4. Fluorite 3. Calcite 2. Gypsum 1. Talc

  37. Moh’s Scale of Hardness Steel nail 5.5-6.0 Fingernail 2.5 Copper coin 3.0 Window glass 5.0 Everyday objects can be substituted for minerals on Moh’s scale

  38. Testing For Hardness Try to scratch mineral specimens with substances of known hardness If a mineral is not scratched by your fingernail, but is scratched by a copper coin then it will have a hardness of 2.5–3.0 If a mineral cannot be scratched by steel it has a hardness of over 6.0 Gypsum is scratched by a fingernail, hardness <2.5

  39. 5. Cleavage The way the mineral breaks Cleavage—minerals break along smooth, flat surfaces and every fragment has the same general shape due to how atoms are arranged in the crystals of a mineral Mica is a mineral that splits easily along a flat surface Physical Properties of Minerals(can be used to identify the mineral)

  40. Cleavage • The way a mineral breaks when struck by a hammer • Cleavage is controlled by lines of weakness in the atomic structure of the mineral • Minerals can have 1, 2, 3 or 4 planes of cleavage • 1 plane, parallel or basal cleavage • 2 planes of cleavage that intersect at a characteristic angle • 3 planes (cubic, rhombohedral) • 4 planes, octahedral cleavage

  41. 6.Fracture The way the mineral breaks Fracture—minerals that break at random with rough or jagged edges Fracture is only described when the mineral has no cleavage Physical Properties of Minerals(can be used to identify the mineral)

  42. Types of Fracture Conchoidal – Like Glass Even – Flat fracture surface Uneven – Irregular fracture surface Hackly – Very jagged like cast iron

  43. Conchoidal Fracture This type of fracture is the same as that shown by window glass A series of concentric curved lines can be seen on the fractured surface A diagnostic property of the mineral quartz 5mm Rose quartz showing conchoidal fracture

  44. Cleavage or Fracture? 1. 4. 3. 2.

  45. 7.Crystal Form or Habit Amorphous Chalcopyrite Crystallised Iron Pyrite Results from the way in which the molecules of mineral pack together.

  46. Crystal form or habit • The external shape of a crystal or groups of crystals is displayed / observed as these crystals grow in open spaces. • The form reflects the supposedly internal structure (of atoms and ions) of the crystal (mineral). • It is the natural shape of the mineral before the development of any cleavage or fracture.

  47. Crystal form or habit • Examples include prismatic, tabular, bladed, platy, reniform and equant. • A mineral that do not have a crystal structure is described as amorphous. • The crystal form also define the relative growth of the crystal in 3 dimension which are its length, width and height

  48. Identify the crystal form of the following needle-like habit bladed habit - Tabular /cubic or equant

  49. Variations in Habit/Form/Appearance of Minerals

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