PREHNITE

This article appears in Volume V22, Page 277 of the Encyclopedia Britannica.

Encyclopedia Britannica - Main :: POL-PRE

PREHNITE , a

mineral

MINERAL

consisting of calcium hydrogen orthosilicate, H2Ca2Al2(SiO4)3. It crystallizes in the hemimorphic class of the orthorhombic system, but the hemimorphic character is usually obscured by twinning. Crystals are generally platy in habit, but they rarely occur singly and distinctly shaped; almost invariably they are closely aggregated together to form barrel-shaped or globular groups with a crystalline surface. This form, together with the

pale

PALE (through Fr. pal, from Lat. palms, a stake, for paglus, from the stem pag- of pangere, to fix; " pole " is from the same original source)

oil-green colour, gives the

mineral

MINERAL

a very characteristic

appearance

APPEARANCE (from Lat. apparere, to appear)

. It is translucent and has a vitreous lustre. The hardness is rather over 6 and the spec. gray. 2.802.95. Crystals are pyro-electric. Prehnite is sometimes classed with the zeolites, since it occurs under the same conditions as these minerals and often in association with them: the small amount of water (4.4%) is, however, expelled only at a red heat and is therefore not water of crystallization.
Prehnite occurs as a mineral of secondary origin in the amygdaloidal cavities of basic igneous rocks, such as basalt and diabase, and less often, in veins in granite and gneiss. Fine specimens are found with zeolites in the volcanic rocks of several places in the

south

SOUTH
SOUTH, ROBERT (1634–1716)

Scotland

, e.g. Old Kilpatrick in Dumbartonshire, Bishopton in Renfrewshirc, Campsie Hills in

Stirlingshire

STIRLINGSHIRE

and in the neighbourhood of Edinburgh; also at Paterson and Bergen Hill in New

Jersey

JERSEY
JERSEY, EARLS OF

, and with native copper in the trap-rocks of the Lake Superior region. In the French (at Le Bourg d'Oisans) and Tyrolese Alps it occurs with

axinite

AXINITE

epidote

EPIDOTE

, felspar, &c., lining crevices in gneiss. Large masses have been found at Credock in Cape Colony, from which locality it was brought in the 18th century by Colonel Prehn, the

governor

GOVERNOR (from the Fr. gouverneur, from gouverner, O. Fr. governer, Lat. gubernare, to steer a ship, to direct, guide)

of the colony; hence the names " Cape chrysolite " and prehnite (of A. G. Werner, 1789). Prehnite is sometimes cut and polished for small ornaments; it then somewhat resembles chrysoprase in

appearance

APPEARANCE (from Lat. apparere, to appear)

.

End of Article: PREHNITE

If you wish, you can link directly to this article.

<a href="http://jcsm.org/StudyCenter/Encyclopedia/POL_PRE/PREHNITE.html">
PREHNITE
</a>

(Previous)
PREFECT (prefet)

(Next)
PREJUDICE (Lat. praejudicium)

JCSM was founded in 1997 and exists to help the community and bring people into a life-changing and productive relationship with Jesus Christ. JCSM offers over 200,000 free web pages, including its weekly inspirational emails that were sent continuously for over a decade.

Jesus Christ Saves Ministries
P.O. Box 9297
San Diego, CA 92169
1-888-887-0417 or Email