what is the difference between rock and stone?
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Rocks are rocks, and stones are included here. Stones we tend to think of as something that we desire, whether is be for jewelry or for putting along your flowerbed while rocks are sort of all encompassing. Really though, there is no difference, stones ARE rocks.
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There was a Bishop Ussher who, by following the time line of the Bible genealogies, determined that the earth to be about 10,000 years of age.  What you are taught in school is a point of interest.  The age of rocks are determined by the types of bones found in them.  The age of the bones by the rocks they are found in.  Who was there in the beginning in order to give the first age.  Modern ages are all guesses.  Yours is probably better than theirs - can't be worse.
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While they can be equal in hardness one would normally find that the granite, being of igneous origins, is more chemically bonded and therefore more difficult to break apart.  However, the individual minerals within the granite may be harder or softer than the sandstone which is usually composed of quartz which has a hardness of 7.  If the sandstone is porous, it will not take extreme cold well at all as any moisture inside the pores will freeze and thereby facture the rock.The granite doesn't have this problem.
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Gemstones relate to Chemistry by the rate at which they form and where they form. This is in direct relation to Geology. Go to your local library and find books that are in the Geology section and then look in the index for the gemstones you have chosen to talk about.
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One way to distinguish between intrusive and extrusive igneous rocks is to observe the crystal size.\nRocks formed below groung (intrusive) have must longer to cool, resulting in a larger crystal size.\nOn the other hand, rocks formed above ground (extrusive) have a much smaller crystal size
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Sedimentary Rocks usually have layers and are made up of pieces of other rocks. The grain size that makes up the sedimentary rocks can be of any size. Microscopic as in silt, small as in sandstone and large as in conglomerate.
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In a phrase, volcanic rock.\n\nEach volcano erupts constructively and destructively, and some of those constructive eruptions build the sides of the volcano.  The type of magma determines the color and shape.
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Lithology is the study of rocks and minerals.  Stratigraphy is the mapping of layers of sediments, perhaps composed of rocks of similar types.
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the simplest explanation is as follows:\n\n* igneous rocks are formed when molten lava is erupted on to the earth's surface and cools. i.e. basalt lavas. \n\n* sedimentary rocks are formed when other rocks (possibly igneous, metamorphic or previous sediemtnary rocks) are eroded chemically or physically and are then redeposited. i.e. sandstones and mud stones.\n\n* metamorphic rocks are formed when other rocks (igneous or sedimentary typically) are buried and then exposed to high temperatures and pressures that change the properties of that rock. i.e. marble - metamorphosed limestone.
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What you are observing is the oxidation and weathering of a rock. The outside of the rock is exposed to the elements and gets bleached out, the inside is protected by the outer layers.
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stone (st) \na traditional British unit of weight, rarely used in the U.S. Originally the stone varied in size, both from place to place and according to the nature of the item being weighed. A stone of sugar was traditionally 8 pounds, while a stone of wool could be as much as 24 pounds. Eventually the stone was standardized at 14 pounds avoirdupois or approximately 6.350 29 kilograms -- a convenient size because it makes the stone equal to exactly 1/2 quarter or 1/8 hundredweight. Today the stone is used mostly for stating the weight of persons or animals. No -s is added for the plural.\n\nfortnight \na traditional English unit of time equal to 2 weeks or 14 days. The word, a contraction of "fourteen nights," has been used since at least the 1100s.
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A stone is a UK (United Kingdom) measure of weight. 14 pounds equals one stone
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its a rock...\n\npencils...
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Metamorphic rocks are already existing rocks that change under heat, pressure or in chemical reactions (usually underground). Examples are Gneiss (that froms from Granite), Slate (formed from Shale), and Quartzite (formed from Sandstone).\n\nSedimentary rocks are rocks made from sediment (haha makes sense, no?) which can be both organic (fossils!) or inorganic. They are formed into a solid rock through a variety of different forces, including erosion, deposition, compaction, and cementation. There are 3 major groups of sedimentary rocks, which are clastic (formed from the compression of rock fragments), organic rocks (Key word: ORGANIC, aka the remains of plants and animals), and chemical rocks (formed when a solution dissolves, & minerals are left behind). Examples:\nClastic: Shale, Sandstone, Conglomerate, and Breecia\nOrganic: Coal, Limestone\nChemical: Halite, Gypsum\n\nIgneous rocks are formed from magma or lava. They are classifed according to where they were formed-- extrusive rocks are formed from lava on Earth's surface, while intrusive rocks are formed from hardened magma beneath Earth's surface. Texture and mineral composition are also factors of classification. Examples include granite (which is extremely abundant), Rhyolite, Pegmatite, Porphyry, Basalt, Pumice, and Obsidian.
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Igneous rocks are formed when molten rock (magma) cools and solidifies, with or without crystallization, either below the surface as intrusive (plutonic) rocks or on the surface as extrusive (volcanic) rocks. This magma can be derived from either the Earth's mantle or pre-existing rocks made molten by extreme temperature and pressure changes. Over 700 types of igneous rocks have been described, most of them formed beneath the surface of the Earth's crust. The word "igneous" is derived from the Latin ignis, meaning "fire".
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* Igneous Rocks\nIgneous rocks are called fire rocks and are formed either underground or above ground. Underground, they are formed when the melted rock, called magma, deep within the earth becomes trapped in small pockets. As these pockets of magma cool slowly underground, the magma becomes igneous rocks. \n\nIgneous rocks are also formed when volcanoes erupt, causing the magma to rise above the earth's surface. When magma appears above the earth, it is called lava. Igneous rocks are formed as the lava cools above ground.\n\n* Metamorphic Rocks\nMetamorphic rocks are rocks that have "morphed" into another kind of rock. These rocks were once igneous or sedimentary rocks. How do sedimentary and igneous rocks change? The rocks are under tons and tons of pressure, which fosters heat build up, and this causes them to change. If you exam metamorphic rock samples closely, you'll discover how flattened some of the grains in the rock are.\n\n* Sedimentary Rocks\nFor thousands, even millions of years, little pieces of our earth have been eroded--broken down and worn away\nby wind and water. These little bits of our earth are washed downstream where they settle to the bottom of the rivers, lakes, and oceans. Layer after layer of eroded earth is deposited on top of each. These layers are pressed down more and more through time, until the bottom layers slowly turn into rock.
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rocks are made up of minerals