limestone classification

[lithicbeads]

   This is taken verbatim from  Bulletin No. 52 of the Washington Division  Division of Mines and Geology  " Limestone Resources of Western Washington " by Wlibert R. Danner who is a big deal in geology here.
   
   " Classification based on major impurities

   Many of the impurities within a limestone are deposited along with the calcium carbonate at the time of formation, but some of them may chemically replace the limestone during and after it's deposition. When the limestone impurities are sufficiently abundant to be visible , a classification may be established that is based on their composition .

   Argillaceous limestone contains a high proportion , up to 50 per cent of clay ( argilaceous) or shaley material interbedded or mixed with the limestone.If over 50 per cent argillaceous material is present , the rock may be a calcareous shale or calcareous mudstone.

   Siliceous or cherty limestone is limestone interbedded with ribbon chert or partially replaced with secondary chert ( jasperoid) or flint ( a black and translucent variety of chert).

   Ferruginous limestone contains iron oxides in sufficient amount to give the limestone a yellowish or reddish color.

   Bituminous limestone contains hydrocarbon material in sufficient amount to color the limestone  dark grey or black.Often this type of limestone gives off a strong bituminous or oily odor when freshly broken. More rarely , a dark colored limestone may be carbonaceous  and contain carbonized fragments of vegetation.

   Arenaceous limestone contains abundant quartz grains.

   Tuffaceous limestones contain abundant small fragments of ash and volcanic rock. "

[helens]

Ok, so when something is called 'limestone'... because of the other compositions, it can be from 3-7 hardness right?

The biggest puzzle to me is why use 1 generic name, limestone, to cover a mineral that crosses so many hardness classifications. It's like skipping the name diamond and calling everything from diamond to graphite to coal say carbon. It's all carbon, but no one would do that.

 I'm in Florida, so of course, we have tons of limestone, since this IS the land of limestone, and where much of the limestone in the whole country comes from. Uh... it's not hard. So it threw me when you guys started talking about how hard limestone is. The terminology doesn't make much sense to me... anymore than calling the diamond in an engagement ring graphite or a lump of coal. I wonder why the geologists did that?

[sealdaddy]

Thanks, Frank~

[lithicbeads]

Limestones formed adjacent to large expanses of flat land with low gradient streams and limestone formed in seas with large shallow expanses would be unlikely to be hard. Our coastal limestone here in the west were formed adjacent to volcanoes jutting out of deep ocean so they got lots of silica from deep water diatoms and much silica from the steep and quickly eroding volcanoes.
These island arcs docked against B.C. , Alaska , Washington , Oregon and California bringing their unique reef and back arc basin geology( sediment based) mixed with the sea bed geology that collided with them to make all  of the coastal west.

[sealdaddy]

How about that Very hard layered TX river rock limestone I cut and showed a few months back, Frank?

[lithicbeads]

 there were huge fresh and salt water oceans in the interior east of the rockies. The big freshwater oceans get diatom layers that are hundreds of feet thick at times  , you can see them here in Washington in the central basin opal deposits so it could be silica from that source or salt water diatoms . They also could be arenaceous limestones as there were tall mountains with silica to your west but the diatom s are most likely. What is very confusing is the situation in Nevada as the mining company geologists use the term jasperoid for many deposits there that they grind up for the gold content  yet they are supposed to be rare .

[DavidS]

... I'm in Florida, so of course, we have tons of limestone, since this IS the land of limestone, and where much of the limestone in the whole country comes from. Uh... it's not hard. So it threw me when you guys started talking about how hard limestone is...

Not sure if this helps but here is some more info on Limestone....

As a former broker and fabricator of architectural stone, a strong majority of projects along the eastern seaboard utilize Indiana limestone.  In laymens terms, once you dig past a few feet of the surface/cull layers, the stone is made of small and tight or dense grains.  The grain pattern, color, and hardness change as you quarry deeper in ground.  (See color quarry charts, section views, & geological info by searching "Indiana Limestone Handbook."   Many of the limestone stone quarries in Florida a large grain or large shell compacted with significantly more air pockets, whether visible or microscopic.  The stone is much lighter than Indiana limestone and most FL pieces will crumble if exposed to northern freeze/thaw cycles. 

B/R,   David

[domdeslagons]

Very interesting topic for me who use mainly  limestone I find on the sea shore in New Caledonia! I do confirm some are quite hard and some very soft. If you are not lucky in a same piece you can have both and then you get a headache trying make something nice out of it!
Some might have seen the little statue I made, lot of different colors. Nice stuff for beginners!
 

[Isotelus]

Here in Ohio we are also a kind of ( Mud Pie ) State, that is we have a lot of sedimentary stone and a lot of those are limestones. When I was just learing to cut cabs back when I was 8 or so that was about all there was  to cut. Then I learned some of the fossil corals found in the limestones made interesting cutting. Especially the few that were silicified- but most were not and a lot of the colors were kind of plain. Every once in a while a banded chert nodule would show up that had weathered out of the local Marble Cliff or Columbus limestone. Those were always welcome to a bored young cutter such as myself in those days.