A headstone changing color is typically due to environmental and chemical factors affecting the stone’s surface over time. Here are the most common reasons:

Weathering & Moisture

Rain, snow, and humidity can penetrate porous stone like marble or limestone. Water carries minerals and pollutants that can leave stains or the appearance of a color shift.

Biological Growth

Algae, lichen, moss, or mold often grow on headstones, especially in damp or shady areas. These organisms can produce green, black, or orange discoloration on the surface of the headstone.

Air Pollution

Pollutants like sulfur dioxide or acid rain can react with certain minerals in the stone, especially in urban or industrial areas, causing yellowing or darkening on the granite headstone.

Oxidation

If the headstone has metal components or is near iron-rich soil, rust can leach into the stone and turn it reddish or brown, also the hard water from cemetery.

Cleaning Products or Sealants

Past treatments, especially improper cleaning agents or sealants, not meant for outdoor use, can sometimes discolor over time or react with natural stone.