Graphic Feldspar Identification Guide

What Graphic Feldspar Looks Like

Graphic feldspar is alkali feldspar (usually microcline or orthoclase) that contains a regular intergrowth of quartz forming angular, wedge-shaped figures resembling ancient runes or cuneiform writing — hence "graphic." The feldspar host is typically pink, cream, or grey, and the embedded quartz appears as darker, glassy, V-shaped or rod-like markings that share a common crystallographic orientation. On a freshly broken or polished surface the quartz wedges all wink with light together when you tilt the specimen, because they are part of one continuous quartz crystal threaded through the feldspar.

Step-by-Step Field-ID Checklist

1. Look for rune-like markings. Angular, repeating quartz wedges in a feldspar background are the defining feature.
2. Tilt the specimen. All the quartz figures should flash light simultaneously, confirming a single intergrown quartz orientation.
3. Identify the host. The matrix should show feldspar cleavage — flat, reflective faces at near-right angles.
4. Test hardness. Both feldspar (6) and quartz (7) scratch glass.
5. Confirm pegmatite context. Graphic feldspar is a coarse pegmatite texture, so grains are large.

Key Diagnostic Tests

• Hardness: Feldspar 6, quartz 7 — the rock scratches glass.
• Cleavage: The feldspar host shows two good cleavages; the quartz wedges show none.
• Optical flash test: Quartz figures extinguish/brighten together when rotated — diagnostic of graphic intergrowth.
• Acid test: No reaction with dilute HCl.
• Streak: White.

Common Look-Alikes and How to Tell Them Apart

• Graphic granite: Essentially the same material described at rock scale; "graphic feldspar" usually emphasizes a single large feldspar crystal showing the texture, while "graphic granite" describes the whole pegmatitic rock. They are the same intergrowth phenomenon.
• Ordinary granite: Granite has separate, randomly arranged quartz and feldspar grains; graphic feldspar has quartz systematically threaded through one feldspar crystal in a repeating pattern.
• Perthite: Perthite shows feldspar-in-feldspar exsolution (wavy films), not angular quartz wedges; the markings are paler and irregular.
• Runite weathering / dendrites: Manganese dendrites are surface, branching, and black; graphic quartz figures are three-dimensional, glassy, and angular.

Where Graphic Feldspar Is Found

Graphic feldspar forms in granitic pegmatites, often in the intermediate zones where quartz and feldspar crystallized together. It is widespread in pegmatite districts worldwide, including New England and the Black Hills (USA), Scandinavia, Russia, Brazil, and Madagascar. Search pegmatite dikes, feldspar quarries, and pegmatite dump material.