FMF - Friends of Minerals Forum, discussion and message board

[trtlman]

I have seen many types of countertops that are called granite. Most of them are a mix of black minerals. When I think of granite I think of the classic black and white granite which are the most common granite countertops I have seen. I was wondering are there different types of granite other than the classic black and white granite?

[rockman]

No...Granite does not come in black naturally.
It may be black carrara marble from China.

[Mark Ost]

Granite is a bit of a broad term for a range of intrusive rocks. Some are black and white as you say but some can be quite red if enough Orthoclase feldspars are in the make up. Colorado has very red granites. If they have sufficient biotite content then they may be darker.

[Steve Maslansky]

A good reference to see the myriad of materials used is "The Sourcebook of Decorative Stone" by Monica Price. Firefly Books. Should find it on Amazon.

[GneissWare]

If the specific question is "Are Granite Countertops Always Made of Granite?"
Yes, by definition.

If the question is "Are stone Countertops Always Made of Granite?"
No. They are made of marble, granite, gneiss, conglomerate, and basically anything that has some structural integrity (either naturally or induced by stabilizers).

[trtlman]

Thanks everyone, this is something I been curious about for a while now. Every time I watch one of the home improvement shows they would use granite countertops.

[Mark Ost]

Yep
Just don't take counter tops for granite!

[Bob Hartzell]

Granite is the trade name for any dimension stone composed of minerals that are mostly harder than glass. Marble is the trade name for dimension stone composed of minerals softer than glass (that is why your mother told you not to put your glass down on her marble-top table). Most "granite" is not granite. Much "marble" is not marble, e.g. the famous, brown Tennessee Marble is limestone.

[Bob Hartzell]

Granite is the trade name for any dimension stone composed of minerals that are mostly harder than glass. Marble is the trade name for dimension stone composed of minerals softer than glass (that is why your mother told you not to put your glass down on her marble-top table). Most "granite" is not granite. Much "marble" is not marble, e.g. the famous, brown Tennessee Marble is limestone.

[Roger Warin]

In Belgium, "petit granit" is a limestone rock, blue color black, with fossils, many crinoids.
When the rock is broken, it exudes a smell of sulfur.

Belgian blue limestone
Also known as / varieties
Blue stone, Petit granit - Pierre bleue de Belgique®.
Extraction zone
Basins of Soignies, Ourthe-Amblève and Bocq, provinces of Hainaut, Liège and Namur.
Mineralogical composition
Calcite ± 96 %, traces of dolomite, quartz and pyrite.
Maximum dimensions of rough blocks
Length 4,5 m; width 2,5 m; thickness 2,5 m.

Roger.

[newryqs]

Just to add to the discussion. "Black granite" is a trade term for a wide variety of nearly black coarsely crystalline rock used for ornamental purposes: facings, counter tops, etc..

Best Wishes, Van

[Josele]

Just to comment that right now in Spain and many other countries most countertops instaled in new houses are made with Silestone, a compound with 95% of quartz grains agglomerated with resin. It is available in many colors and textures, some of them very granite-like.

...although I still prefer the white marble

[prcantos]

To illustrate the wide use of the term 'granite' to call some useful rocks, you can visit this thread in the Spanish-side FMF, which contains both technical and trade names:

Brazilian ornamental rocks.

(Use the Google-translation function if necessary). Enjoy it!

[John S. White]

Countertop dealers are really lazy and they simply do not care to deal with the intricacies of the stone world so they recognize very few types of stone, usually only granite, marble, serpentine and slate, no matter what the materials actually are. Black granite may actually be labradorite. Much that is sold as granite is actually gneiss and as stated above much marble is really limestone. If the rock has a wavy pattern throughout it is probably gneiss, which is a very adequate substitute for granite as it is compositionally very similar to granite.

Another widely used misrepresentation is that granite countertops need sealants, that is an expensive chemical that is supposed to keep it from staining. Real granite does not stain and does not require sealing.

[Mark Ost]

All you geologists and chemists should have been interior decorators from the looks of things!

[Jordi Fabre]

[Woody Thompson]

Hi Jordi,

Thanks for rescuing my posting above. I wondered why it didn't appear, but maybe had a typo error in "houses" or whatever it was that provoked the automatic spam response?

Regarding the necessity of sealing granite countertops, maybe there are less solid granites in some quarries, that are not fresh and solid and may have a little porosity or weakened grain boundaries. Even here in glaciated New England, the Conway Granite (famous for its crystal-bearing miarolitic cavities) is so crumbly in places that you can excavate it with a shovel.

Cheers,
Woody Thompson

[Jesse Fisher]

The study and classification of rocks (known as "petrology") is a branch of the geological sciences that employes a complex and and often arcane terminology, perhaps rivaled in the other sciences by molecular biology. I don't think one can expect a manufacturer or salesman dealing in dimension stone to know the difference between a granodiorite, a quartz monzonite, a gabbro or an anorthosite, so they all just get the generic name "granite" regardless of whether the rock is a true granite or not. I don't expect that many even know the difference between an igneous and a metamorphic rock, so all manner of schists get labeled "granite" as well.

I suspect that the number of geologists with any petrological training is very very small within the population of potential customers for these things, so I seriously doubt that the average buyer of stone counter tops knows or cares about the differences either. I'm sure all they want is something durable and pretty.

Being a member of that "very very small" group, I sometimes enjoy going through the sales samples at tile and counter top dealers, looking for interesting rock types and, I'm sure, boring any poor salesman that happens by with the details. I once recall finding a stone that was a quartz-mica schist with thousands of little red garnet grains in it. About the time I got to speculating on what these must have done to the sawing and polishing equipment, I think the salesman heard his mother calling!

[Jordi Fabre]

[John Medici]

Just a note on a recent stone countertop my family purchased. All salespeople we talked to called everything in the establishment "granite". The one we chose was definitely not granite or marble. It was mainly black swirls with some swirls and splotches of red (a combination of hematite and magnetite) with irregular veins of white quartz interspersed in it. On questioning a supervisor or two while trying to avoid being a pest, I came to the conclusion that it may have come from an iron mine (or stone slab mine) in Brazil. This may or may not be the case, but we have enjoyed having it, and one can take a magnet to it to find the zones of magnetite.