STONE FACTS;

should answer the most basic questions . . .


WHAT IS MARBLE, LIMESTONE, TRAVERTINE, SLATE & GRANITE?

1) Limestone and Marble begin as the same material. Marble is simply changed limestone, or to use the technical term, metamorphic limestone.

Limestone is the result of millions of years of sea shells and bones of sea creatures settling as sediment on an ocean floor (hence it is called a sedimentary stone). The calcium in the bones & shells combines with Carbon Dioxide in the water to form Calcium Carbonate, which is the basic mineral structure of all limestone and marble. Less than 3% of the stone is the color, which is simply other natural elements present when the stone formed (ie iron deposits give you a reddy brown).

Given enough heat and pressure, limestone will crystallize, resulting in marble. The crystal structure allows marble to take a polish, and bring out the color of the other trace elements. Limestone, not being crystallized, will not polish.

2) Travertine also began as limestone, which over time, through geological shifting, has found its way deep in the Earth. The porous nature of limestone makes it a great reservoir for liquids. Aquifers, which are the enormous underground pools of water that feed our wells and water our cities, are the remnants of ice age melting, which sank below and was absorbed by limestone. Heated by the Earth's inner core, the water rises as steam and hot pressurized water, to form hot mud baths, "Old Faithful", " Mammoth Springs", and other gizers. This rising hot water, disolves the limestone and brings with it granules from below, forming mud beds on the surface. If enough time transpires, and the mud beds cool, they will crystallize into solid stone called travertine.

3) Granite began as the liquid magma in the center of the Earth. As a result, it is a different type of stone, called Igneous. Due to the extreme pressure within the Earth, and the absence of atmosphere, granite is formed very dense with no pores. Granite is really a host of ingredients, including common minerals like feldspar, quartz and mica, and the proportions vary considerably from deposit to deposit. The major mineral component of granite is feldspar. Quartz, which is the hardest part of Granite (it ranges from 70% to 80% the density of a diamond) comprises only between 10-30% of the rock, whereas feldspar (potassium and sodium varieties) makes up 60-80%. (This contrasts dramatically with GRANIREX, which is 93% natural Quartz).

4) Slate is metamorphic rock, like the marble. However, instead of forming from a pre-existing limestone (like marble), slate is formed from the low-grade metamorphism of the sedimentary rock shale. Slate, like shale ("mudstone"), is a very fined-grained rock of mostly microscopic clay minerals with some microscopic quartz and calcite. Slate can also contain some of the same minerals found in granite, which make some slates iridescent and/or hard. The alteration of shale by heat and pressure produces the pronounced partings (slaty cleavage) that give slate its characteristics. Like limestone and marble, the color comes from trace metals. The wild colors on most Chinese and Indian slates are the result of splitting the slate along natural layers, which exposes the metals to the atmosphere, and they oxidize (rust).

WHAT IS POLISHED, HONED, FLAMED AND SAWCUT?

1) Polishes on stone are a change in the surface of the stone itself, not anything applied to the surface. A polished stone is 100% stone, and nothing else.

Only crystallized stone can take a polish. Essentially, at a microscopic level, the factory is putting a facet on each crystal, much as a jeweler puts a facet on a diamond. The result is the same; a surface which allows light to reflect in and out of the stone in a parallel way, which enhances the visible light and color, and gives the appearance of depth.

A polished finish does not affect the porosity of the stone.

2) Honed finishes are smooth, like a polish, but are non-reflective. This can be achieved three ways;

Note; Stones are polished by diamond studded pads which are applied with pressure and usually water and some thick compound to keep the stone cool. The amount of pressure, the type of pad, the grain count of the diamonds (like the grain count of sandpaper), and the liquid mediums all depend on the particular characteristics of the stone. For instance, GRANIREX must be kept very cool when polishing, or the epoxy will burn, and the color will disappear.

3) Flamed, or sometimes called thermal, is a molten surface which is the result of applying direct flame at high temperatures (a blow torch). This usually is seen in granites and some limestones. Most stones cannot withstand this treatment. GRANIREX simulates the surface, and calls it "textured".

4) Sawcut finishes are the most unfinished, since this is the surface of the stone when it is first cut, without any treatment. It is a slightly rough surface, usually with circular saw cut marks. Most tumbled marble is made from sawcut material, and if not tumbled quite enough, will still show a bit of this finish. One rarely seas sawcut material sold directly to the consumer.


to return to THE CHRIS JOHNSON HOME PAGE
(C) 1998 THE LINLEY COMPANY (Chris Johnson)