Datolite - Gem Sea-Green Crystal on Prehnite, Lane Quarry, Massachusetts

Datolite from the Lane & Son traprock quarries at Westfield, Massachusetts, is one of the touchstone American classics, and this piece sits at the upper end of what those basalt cavities ever produced. A single glassy crystal of 4 cm dominates the specimen, pale sea-green and gemmy, resting on a bed of pale prehnite. Crystals of this size with this degree of transparency and face quality are uncommon from Lane, and uncommon from anywhere. The architecture is the familiar short-prismatic, wedge-like Datolite habit, with the monoclinic faces meeting at crisp angles and terminating cleanly at the top; the lower end is not terminated, as it grew into the prehnite. The dominant crystal stands proud of the matrix and reads strongly in the round rather than lying flat against it. A partially complete sidecar crystal of about 2 cm sits at the base on the reverse, giving the group a secondary point of interest and the sense of a natural growth sequence rather than a single isolated individual. Colour is the quiet strength here. In reflected light the crystal reads as a soft celadon, almost greenish-ivory, deepening where the body is thickest and paling toward the thinner terminal faces, which transmit light with a faint yellow-green cast. Internally, clouds of fine inclusions and growth-mottling float through the crystal like frost on glass, catching the light as a scatter of silvery flecks. The prehnite beneath runs from very pale green to off-white, a shade removed from the Datolite and just enough to set it apart. Lustre is high and vitreous, verging on glassy on the principal faces. Turned under a directional lamp, the broad terminal face flashes as a single bright plane, while the striated and stepped faces below break the reflection into fine parallel bands and chevrons -- subtle growth structure that only emerges at particular angles. The matrix contributes more than support. It is vaguely botryoidal where it meets the Datolite, mostly granular and massive behind, but across the front and centre it carries a sparkling druse of fine white crystals that lifts the aesthetics considerably and frames the gem crystal. Condition is reported as a single small ding near the termination toward the rear, hardly noticeable in display position. Datolite is brittle, and the projecting edges and broad terminal faces of a crystal this size are precisely what gets bruised in a quarry environment; preservation at this level is a material part of the piece's standing. At 6.5 x 5.7 x 4.0 cm this is a small cabinet specimen with the visual weight of something larger, the Datolite occupying most of the front face. Provenance runs through the Richard Gaines and George Loud collections. Under a single light it glows from within, cool and green.