Hi Joanie If I understood your question right, I might have the answer and I think others might be interested as well. Last year I struggled with a similar problem and found a way of plotting 3-component data on an X-Y scatter diagram in Excel. Suppose you have 3 components A, B and C. Let's say you have mineral analyses expressed in terms of these components only (or projected onto these 3 components). This gives a triangle with apices A, B and C. The trick is now to transform the triangular coordinates into (x, y) coordinates. If you locate the A apex at (x, y) = (0, 0), the B apex at (1, 0) and the C apex at (0, 0.5 SQRT3), the transformation required is: x = 0.5 * C + B y = 0.5 SQRT3 * C (in the above lines, SQRT3 is the square root of 3) After transforming the data, you can plot the datapoints plus the 3 apices onto an X-Y scatter diagram. You can then print the diagram and draw the sides of the trangle by hand, or you export the data to a drawing program compatible with Excel (I use MacDraw) and finish the triangle there. I hope this helps you. Best regards, Leo --------------------------------------------------------------------------- Leo M. Kriegsman Professor of Geology and Mineralogy Department of Geology fax: +358 2 333 6580 University of Turku tel: +358 2 333 5481 20014 Turku, FINLAND e-mail: [log in to unmask] ---------------------------------------------------------------------------