Where is Quartz with Feldspar found?
SiO2 (Quartz) and (K,Na)AlSi3O8 (Feldspar)
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Open the appQuartz with Feldspar occurs in specific geological environments. Knowing where to look, and in what kind of rock, is the difference between going home empty-handed and finding a great specimen.
Where to find Quartz with Feldspar
Worldwide
As major rock-forming minerals, quartz and feldspar are found globally in regions with significant igneous, metamorphic, and sedimentary rock formations. Notable occurrences for large crystals or specific varieties include Brazil (quartz), Madagascar (feldspar, quartz), Russia (quartz), and the United States (various states for both, e.g., Colorado, North Carolina, California).
Continental Shields and Cratons
These ancient, stable parts of continents are rich in granitic and gneissic rocks, which are primary hosts for quartz and feldspar.
Mountain Ranges
Areas of active or past orogeny (mountain building) often expose large volumes of igneous and metamorphic rocks containing these minerals.
Sedimentary Basins
Mature sedimentary basins can contain sandstones and arkoses rich in detrital quartz and feldspar grains, eroded from older igneous and metamorphic sources.
Collecting tips
- Look for Granitic Outcrops. Granite is an excellent place to observe quartz and feldspar together. Quartz will appear as glassy, often gray or colorless grains, while feldspar will be opaque, typically white, pink, or salmon-colored, with distinct cleavage planes.
- Examine Metamorphic Rocks. In gneisses, quartz and feldspar often form alternating light-colored bands. Look for the characteristic glassy luster of quartz and the blocky, cleavable nature of feldspar.
- Check Sedimentary Rocks. In sandstones, quartz grains are typically rounded and clear, while feldspar grains may be less rounded and exhibit a duller luster or faint cleavage. Arkose will have a noticeable pinkish hue due to abundant K-feldspar.
- Hardness Test. Quartz (Mohs 7) will scratch glass and steel. Feldspar (Mohs 6-6.5) will scratch glass but may be scratched by quartz. This is a key differentiator between the two in hand samples.
- Cleavage vs. Fracture. Feldspar's distinct cleavage (smooth, flat surfaces) is a critical identifying feature, contrasting with quartz's conchoidal (shell-like) fracture and lack of cleavage.
Quick Check
- Color:
- Quartz: Colorless, white, gray, various. Feldspar: White, pink, gray, green.
- Luster:
- Quartz: Vitreous. Feldspar: Vitreous to pearly.
- Streak:
- Both: White (non-diagnostic for these minerals).
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