Cookeite chlorite: The mineral Cookeite information and pictures

About

Cookeite (pronounced Cook-ite) is an uncommon member of the Chlorite group, and is best known for its occurrence in granite pegmatites associated with Tourmaline, where it often forms as a growth layer upon the Tourmaline. Cookeite is named in honor of Josiah Parsons Cooke Jr. (1827-1894), a Harvard University scientist who was instrumental in the measurement of atomic weights.

Crystal Forms & Aggregates

Crystals, which are always small, are in tabular pseudohexagonal form. Most often in radiating and botryoidal aggregates, as ball-shaped spheres, and in micaceous crusts, flakes, and small rosettes.

Other ID Marks

May have a slightly greasy feel.

Striking Features

Crystal habits, localities, and mineral associations

Environment

As an alteration mineral in lithium-rich granite pegmatites.

Noteworthy Localities

Cookeite is best known from the pegmatite quarries in Oxford Co., Maine. Specific localities there include Mt. Rubellite, Hebron; Mt Mica, Paris; Plumbago Mountain, Newry; the Tamminen Quarry, Greenwood; and the Bennett Quarry, Buckfield. Cookeite also comes from the Gillette Quarry, Haddam; and at the Strickland Quarry, Portland; both in Middlesex Co., Connecticut.

Some of the best bluish and greenish Cookeite, in interesting ball aggregates with Quartz, comes from Saline Co., Arkansas, especially at the Stand-on-Your-Head mine in Bland. Good Cookeite also comes from the Tourmaline mines around Pala, San Diego Co., California; as well as the Tourmaline mines of of Minas Gerais, Brazil, especially at Conselheiro Pena in the Doce valley.