SCOLECITE
The zeolites are a large group of hydrous
aluminosilicate minerals. They typically fill voids in other rocks, usually
basalt lava flows. Below a fantastic spray of scolecite
needles. Scolecite is a calcium zeolite having the chemical formula CaAl2Si3O10·3H2O
(hydrous calcium aluminosilicate). It has a nonmetallic, glassy luster,
is variably colored, has a white streak, is moderately hard (H = 5 to 5.5), and
often forms radiating clusters of acicular crystals.
Various zeolites, including scolecite, are well known
in the vast, thick basalt lava flow succession of western India's Deccan
Traps. The Deccan Traps is a flood basalt deposit. Flood
basalts represent Earth's most voluminous volcanic eruptions. The
Siberian Traps of Permian-Triassic boundary age is the # 1 flood basalt deposit
on Earth, volumetrically. The Deccan Traps dates to Cretaceous-Tertiary
(K-T) boundary time (65 million years ago), and appears to be related to the
K-T mass extinction.
The basalt lava flows of the Deccan Traps sometimes
have vesicles, or voids, representing ancient gas pockets. These voids
often get filled up with zeolite minerals. However, large spectacular
sprays like the specimen shown below are uncommon.
Scolecite from India (CM public display, Carnegie Museum of Natural History, Pittsburgh,
Pennsylvania, USA).