Removing Iron Oxide Stains from Rocks Safely with Oxalic Acid

By Andrew Alden, About.com Guide

Many rocks are stained brown because of the presence of iron oxides. That stain can be gently removed without harming the rock using oxalic acid (C₂H₂O₄). Oxalic acid is the preferred treatment for cleaning stains from quartz and pyrite crystals. It can be used (with care) on carbonate minerals, unlike the hydrochloric acid used in the acid test. Let me show you a typical treatment, starting with this assortment of gneiss specimens.

Previous

• The Rocks: Before Oxalic Acid Treatment
• Put the Rocks in the Acid
• Oxalic Acid Treatment: Day 1
• Oxalic Acid Treatment: Day 3
• Oxalic Acid Treatment: Day 4
• The Rocks: After Oxalic Acid Treatment

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