Which feldspar have striations

Only orthoclase can be pink or blue, and only plagioclase can be dark gray to black. Unfortunately, both can be light in color, and since most feldspars are nearly white we're often still faced with a nasty identification problem. If it's white and has striations, I call it plagioclase.

If it's white but I can't see any striations, it may be either plagioclase or orthoclase. In this case, I just call it feldspar and look for other clues to come up with a name for the rock. What is common to all the feldspars is the same arrangement of atoms, a framework arrangement, and one basic chemical recipe, a silicate silicon plus oxygen recipe. Quartz is another framework silicate, consisting only of oxygen and silicon, but feldspar has various other metals partly replacing the silicon.

The exact composition of the various feldspar minerals depends on what elements balance the oxygen, which has two bonds to fill remember H 2 O? Silicon makes four chemical bonds with oxygen; that is, it's tetravalent. Aluminum makes three bonds trivalent , calcium makes two divalent and sodium and potassium make one monovalent. So the identity of X depends on how many bonds are needed to make up the total of One Al leaves one bond for Na or K to fill. Two Al's leaves two bonds for Ca to fill.

So there are two different mixtures that are possible in the feldspars, a sodium-potassium series and a sodium-calcium series. The first is alkali feldspar and the second is plagioclase feldspar. Alkali feldspar has the formula KAlSi 3 O 8 , potassium aluminosilicate. The formula actually is a blend ranging from all sodium albite to all potassium microcline , but albite is also one endpoint in the plagioclase series so we classify it there.

This mineral is often called potassium feldspar or K-feldspar because potassium always exceeds sodium in its formula. Potassium feldspar comes in three different crystal structures that depend on the temperature it formed at.

Microcline is the stable form below about C. Orthoclase and sanidine are stable above C and C, respectively. Outside the geological community, only dedicated mineral collectors can tell these apart. But a deep green variety of microcline called amazonite stands out in a pretty homogeneous field. The color is from the presence of lead. The high potassium content and high strength of K-feldspar make it the best mineral for potassium-argon dating.

Alkali feldspar is a crucial ingredient in glass and pottery glazes. Microcline has a minor use as an abrasive mineral. The plagioclase feldspars are named according to the following scheme, where the numbers are the percentage of calcium expressed as anorthite An :. Many feldspars are igneous as they commonly precipitate out in magma as it cools.

They may also be formed as metamorphic minerals in veins of other rocks. This process involves both heat and pressure. Finally, over time feldspar can weather to produce sediments. Two main weathering agents include wind and water. A feldspar may be worn down to large grains which then turn into conglomerate or breccia, or it may weather to a special kind of clay called kaolin. Kaolin is a very fine-grained particle. When this rock transforms into a sedimentary rock it is called kaolinite.

It has many pharmaceutical, cosmetic and paper uses. Alden, A. About feldspar. Amethyst Galleries, Inc. The feldspar group. Conjecture Corporation. What is feldspar. Dhavale, G. Kaolin uses. Draggan, S. Teacher Newsletter. Partnership Opportunities. You might also be interested in: Cool It! Game Check out our online store - minerals, fossils, books, activities, jewelry, and household items! Spotting minerals is fun! There are many different types of minerals, each with a different name and a special set of characteristics.

So, if you find a mineral that you do not recognize, you can use Silica Si and Oxygen O are the only elements within pure quartz. If a cooling magma has silica leftover after feldspars form, quartz is likely Granite Rocks Look at granite closely and you can see crystals of common silicate minerals such as quartz, plagioclase feldspar and orthoclase feldspar.

In fact, granite is mostly quartz and feldspar crystals. It also