Bonds between the Si and O ions care covalent cannot be broken apart Since Si

Bonds between the si and o ions care covalent cannot

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Bonds between the Si and O ions care covalent- cannot be broken apart. Since Si and O together make up 75% of the earth’s crust- silicates is by far the most important group of minerals we study. SILICATES - (SiO 4 ) 4- complex ions can link to cations to form minerals. However, they can link directly to other (SiO 4 ) 4- ions to form larger and more complex ions. This direct linkage is called polymerization , and it leads to numerous silicate minerals Silicate subdivisions: Isolated TDA. (SiO 4 ) 4- TDA are not directly linked to each other, but rather through Mg 2+ and Fe 2 +. The mineral group formed is called OLIVINE. TDA LINK DIRECTLY TO FORM A SINGLE CHAIN- (not a mineral that has a negative electrical charge). (Mg 2+ +/Fe 2+ +/Ca 2+ + to form a mineral. The group is called a pyroxene. 2 single chains link to form a double chain. These double chains linked to each other through cations. This group is called AMPHIBOLE - double chains are elongated in one direction, amphibole often occurs in rocks as needle shaped crystals. Many double chains link to form a sheet structure. These sheets linked together through cations. The important ground of minerals is called Mica - often occurs in rocks as sheets. Some sheets are held together by van der Waals bonds, very weak. These bonds can be peeled apart, van der Waals bond like post it notes. Another important mineral group with sheet like structure is clay minerals . Tda can link into 3-D structure (highest degree of polymerization). There are 2 important mineral groups 1) quartz- SiO 2 , 2) feldspars- contain Ca 2+ , Na + , and K + .
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Revision of Silicates (in increasing order of polymerization) 1) isolated TDA- OLIVINE Single chains of TDA linkage- pyroxene Double chains of tda linkage- amphibole Sheets of tda linkage- mica, clays 2-d tda linkage- quartz feldspar. Other complex ions such as sulfates (SO4)4-, carbonates (CO3)2-, phosphates (CO3)2- cannot polymerize hence much simpler important minerals - calcium carbonate CaCO3- calcite - calcium sulfate CaSO4- gypsum - Calcium phosphate- apatite Important diagnostic features - Identifying minerals Chemistry: Iron is the most important. Adds color (red,green,brown,black) to minerals when present, it raises the melting point(along with Mg) and leads to higher density. BONDING TYPE: Covalent bonded minerals are harder to break and have lower densities. Ionic bonded minerals as above but in each case are less so. Van der waals bonds are easily broken, makes minerals soft. Physical properties used 1) Hardness- MOH’s scale 2) Cleavage- break open mineral exploiting plane of weak bonding EX) platy cleavage- breaking mica apart along planes with van der Waals bonding. 3) Density- minerals with covalent bonds have lower density. Presence of iron raises the density of minerals. 4) Crystal form Other less reliable properties: 1) Color- can be very misleading, minor trace impurities changes color considerably.
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  • Spring '08
  • idontknow
  • Atom, Van der Waals, TDA

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