how do u no if a rock is sedimentary, igneous, or metamorphic in origin by looking at the grains.?

Question

the question i have to answer is this:

take a quick look at the brownish building stone used in the construction.

Are they sedimentary, igneous, or metamorphic in origin (HINT: can you see the individual grains? What do they look like?)

Answer 1

Its been 25 years since I've studied this stuff, but let me take a crack:

If you can see grains of sand it is sedimentary. It is made from pieces of old rock (sediments) that have been glued together. It's most likely sandstone or limestone as those are common building materials.

If you see big crystals it is igneuous and cooled underground. Some of the crystals will most likely be black and mirrorlike (mica) others will look like glass (quartz and feldspar). Most common igneous rocks to build with would be granites.

If you can see crystals and they are distorted (i.e squished, broken, etc. ) it is metamorphic. Most likely marble.

Answer 2

Gosh mike, when did you graduate? In 1492? Your statement: "Igneous was molten at formation, it should have no grains visible almost glass like" is very, very wrong. The majority of igneous rocks I have seen have visible grains.
And baybled, your statement, "for metamorphic, there'd be no signs or anything" is very, very wrong also. I have seen many, many metamorphic rocks that showed many signs of events. In fact, my Structural Geology professor, who also was a metamorphic petrologist, used to call high grade metamorphic rocks as "Rocks with a history". And in case you don't think he knew anything about geology I'll tell you he now works for Cornell University.

Many sedimentary and metamorphic rocks are layered. The only igneous rocks I have seen layered are explosive volcanic rocks. Igneous and metamorphic rocks are (usually) crystalline whereas sedimentary rocks are not.

I know that is not much to go on, but this type of identification is a skill that improves as you learn more about geology.

Answer 3

It is just like one identifies cats, dogs and bears etc. or like a problem faced by a person visiting another country and seing fruits that he has never seen in his own country. To be brief, these three types of rocks have a set of characteristic visual properties and mode of occurrence which helped in identifying them into sedimentary, igneous and metamorphic groups. Sometimes it is not that easy to do so particularly in cases of transitional or mixed rocks. The tests are required only when we want to classify the rock further within the Group or want to study further for its genesis details and economic importance etc. thnks

Answer 4

Igneous was molten at formation, it should have no grains visible almost glass like
Sedimentary was laid down in water and should have fine grains more or less weakly held (sandstone, limestone)
Metamorphic underwent great forces which normally allows larger grains to form (visible) but bind them together

Answer 5

hrmm.. doing sats in a few weeks so here's what i'd look for:

for igneous, look for crystals, big crystals means the rock took a longer time to cool, vice versa with smaller crystals.

For sedimentary, look for grains, layers, lines, ect.

for metamorphic, there'd be no signs or anything.

Answer 6

some buildings use obsidian, very rarely (igneous), granite (sedimentary), and shale is metamorphic

Answer 7

lol LMFAO!!


Categorizing rocks is the least of your problems sweety... Go back to 2nd grade and learn to spell!!

Answer 8

http://jersey.uoregon.edu/~mstrick/AskGeoMan/geoQuerry13.html