Veins appear as sharply defined colored streaks, irregular interlacing markings, toevery gradation possible and sometimes with no sharp line of division. 

Veins were formed after the formation of the host stone as a result of geologicalmovement which stressed or shattered the surrounding stone causing fissures, cracksand crevices. Over time super saturated mineral solutions circulated throw these voidsdepositing minerals eventually filling them, resulting in veining variations from hard to soft.  Calcite and quartz veins being the most common. 

In some marbles, veining is a result of the stone being subjected to long periods ofcontinuous stress, causing stress lines. During this metamorphic process a recrystallizationof various accessory minerals generally occurs along these stress lines producing stressveining, which are often wavy and harder than the surrounding marble.

Soft-veins are more susceptible to problems than hard-veins. When a soft-veinedstone is used in high traffic areas these veins have a tendency to be “chewed-out”.In wet, moist areas two types of  problems can result. In a area with repeated wet/drycycles (showers) or wet/damp humid environments some of the veining minerals maybe dissolved, causing a lose of veining minerals, leaving pits or recessed veins. If theveins contain carbonaceous matter (organic matter) or moisture sensitive minerals(iron compounds) these may cause blotches, streaks or color variations to occur.

Some marbles that have histories of these kinds of problems are Creme Marfils, Perlino Rosata, Breccias and some Perlatos, Rosa Verona, Filetto Rosso, Negro Marquina and the Serpentines (green marbles).

The more veining and color variation in a ornamental marble the more brittle and susceptible to breakage even after installation.

Marble, limestone’s and some varieties of slate have veins. Commercial granite-type stones generally do not contain veins.

The variety, depth, richness and play of color is the most obvious feature of stone. This kaleidoscope of color is the result of several different processes. 

With some minerals their color is a fundamental characteristic directly related to their chemical composition, they are said to have inherent coloration. The majority of common rock-forming minerals calcite, calcium and magnesium carbonate (dolomite),quartz, and feldspars are inherently colorless, that is, white or transparent in their purestate. When these minerals exhibit coloration they are said to posses exotic coloration.This results when trace amounts of some pigmenting elements (mineral solutions and gases or organic matter) are absorb during different stages of the mineral or the over all rock formation.

During the metamorphic process when limestone is transforming into marble, the rock mass becomes viscous, like soft plastic, hydrothermal super saturated mineral solutions (water and gases) under great pressure can pass through the mass causing all varieties of exotic coloration to occur…swirls, clouds, mottling, streaks, and bands. 

The reflection of light from the mineral surface also influences the play of colors in stone as well. Two unique affects particular to granite-type stones is a Schiller and  Labradorescence affect.

Schiller...is a peculiar play of light that gives the stone a metallic like luster.  Labradorescence...is the play of light resulting in a series of vivid iridescent colors, usually a brilliant blue or green predominating. Some have referred to it as the…”Butterfly wing” effect.

Some minerals with exotic coloration’s respond to different color wavelengths in light.  The light the stone receives in its setting can be an important factor in highlighting or minimizing these colors and contrasts.

Sunlight is a balanced full-spectrum light, however sometimes it can be so bright that the colors of the stone can be “washed-out.” Incandescent lighting generally gives off warm light at the yellow-red end of the light spectrum, halogen lighting gives a much more controlled, brighter and whiter light producing a more brilliant color rendition at the cooler end of the light spectrum green-blue, and fluorescent lighting can provide color wavelengths in either the full visible light spectrum or in just portions of it.

These minerals have a definite chemical composition and optical qualities, some of which can be altered, affecting the color of the stone under certain situations, gradually or in a relative short period of time. These alterations take place generally in a few ways…naturally…cleaning chemicals.

Naturally : As a result of the chemical weathering processes previously mentioned. The acids involved in these processes will have a fading affect.The ultraviolet rays from the sun will fad stones that contain organic matter as part the coloring agent. Black marble, colored coralstones, travertine’s and limestone are alter this way.

Cleaning Chemicals : Most stones are sensitive to acidic and alkaline  cleaning solutions. Acidic cleaning solutions can have a fading affect. Acids are used to remove rust stains. Those stones whose colors are based on iron compounds can be affected.

Optical qualities of the minerals can also be altered immediately or gradually by etching their exposed mineral surfaces.

Alkaline cleaning solutions in the pH range of 9-12 used frequently can also have a gradual fading effect If not properly rinsed the alkaline salts can buildup in the pores and produce a hazy dulling affect.

Some chemical alterations take place in a high pH setting and will produce permanent changes over time.

NOTE : If aggressive cleaning agents need to be used for restoration cleaning, preliminary testing is mandatory to determine if there will be any potential chemical reactions.

The acid by-products of air pollutants will also fad the colors of stone.