Look for a .zip file specifically labeled for Eaglercraft or Minecraft 1.8.8/1.5.2 (the versions Eaglercraft is based on).
Eaglecraft, a web-based Minecraft client (typically version 1.8.8 or 1.5.2), allows the use of to make common blocks like stone, dirt, and gravel invisible while highlighting valuable ores like diamonds and gold. How X-Ray Packs Work in Eaglecraft eaglecraft x-ray texture pack