igneous and metamorphic

Granitic Pegmatite Intrusion in Host Rock

Pegmatite dike in amphibolite or schist

AI-generated identification · may be incorrect

Identified May 31, 2026More igneous and metamorphic →

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At a glance

Common name: Granitic Pegmatite Intrusion in Host Rock
Scientific name: Pegmatite dike in amphibolite or schist
Category: igneous and metamorphic
Identified: May 31, 2026
Method: Advanced

AI Estimated Value

As a large landscaping boulder, it might retail between $50 to $300+ depending on local landscaping supply prices and transportation costs. As a specimen, a small hand-sized piece showing the contrast would be worth $5 to $15.

Not an official valuation

AI estimate for general interest only — not an appraisal. Actual value depends on condition, provenance, and market demand. Verify with a professional before buying, selling, or insuring.

This identification was generated by AI and may contain errors. Verify important details before relying on them — and never use an AI result to judge whether a specimen is safe to handle. Read the full disclaimer

Physical properties

The lighter area is a pegmatite characterized by very large, coarse crystals, primarily feldspar (pinkish/white) and quartz (gray/glassy), possibly with some mica or dark mafic minerals. Hardness is roughly 6-7 on the Mohs scale depending on the dominant minerals. Luster varies from vitreous (glassy) for quartz to sub-vitreous for feldspar. Cleavage is well defined in the feldspars. The surrounding darker rock is fine to medium-grained, dark gray to black, likely a mafic rock such as basalt, amphibolite, or a dark schist.

Formation & geological history

Formed through the intrusion of late-stage, water-rich magma into fractures in the pre-existing, cooler host rock. The high water content in the magma allowed for rapid crystal growth, resulting in the exceptionally large crystals seen in the pegmatite vein. This process happens deep within the Earth's crust over long geological periods.

Uses & applications

In general, pegmatites can be important sources of rare minerals (like lithium, beryllium), large gemstone-quality crystals (tourmaline, beryl), and industrial minerals (feldspar for ceramics, high-purity quartz). The surrounding rock could be used for aggregate or decorative landscaping stone. This specific boulder is likely used for landscaping or as a decorative piece.

Geological facts

Pegmatites are famous for hosting some of the largest crystals ever found, sometimes measuring several meters in length. The distinct vein clearly visible in this boulder demonstrates cross-cutting relationships, a key principle of geology where the intrusive pegmatite is younger than the darker rock it cuts through.

Field identification & locations

Identify in the field by looking for distinct bands or irregular masses of extremely coarse-grained rock (pegmatite) contrasting sharply with a finer-grained darker host rock. Look for large, interlocking crystals of quartz and feldspar. Found globally in areas with current or ancient tectonic activity, especially in continental shields and mountain belts. For collectors, massive boulders like this are impractical, but smaller hand samples showing the contact zone can be interesting.