Granitized Hornfels Serpentinite Boulder 11 OUTDOOR EXHIBITS Benc hmar k L ook carefully on the ground about 9 m 30 f t to your right and you will see the small bronz e benc hmark GS A 1 1 973 whic h w as established here by the U S Geological Survey USGS It is used by the Survey in its continuing program of pro viding horiz ontal and ver tical controls for land surveyor s and for preparation of topographic maps Inside the front entrance of the build ing you can read the 1 973 let ter from the USGS cer tifying GS A headquar ter s as a permanent benc hmark location The precise location of the benc hmark is 4002 1 453 N 1 051 4 5867 W Its elevation is 531 287 4 f t abo ve mean sea level The surv e ys w ere accomplished b y Edwin Eck el Douglas Hardwick and Sim F arro w US Geological Surv e y Denv er Colorado Gr anitic Specimens The specimens on the w alls next to the main entrance are two types of granitic roc k The specimen on the lef t w all from the Fletc her Mason quar ry in Mason New Hampshire is gray and white granite cut by a pinkish band of pegmatite The specimen on the right w all is a granitiz ed hornfels from the Cornucopia gold mine in Or egon s W allow a Mountains The dark dense fragments are hornfels a metamorphic roc k resulting from contact metamorphism in this case when shales were bak ed by the intrusion of a magma body At one time this entire specimen may have been composed of fractured horn fels The fractures lik ely allowed hot solutions to enter the roc k c hemically altering some of it into granitic roc k The Mason granite is a gift from Richard H Jahns Stanford Univ ersity Stanford California and a for mer president of the Society and James W Sk ehan Boston College Chestnut Hill Massachusetts The hornfels is a gift from GE Goodspeed Univ ersity of W ashington Norw egian Blue P ear l Door Pulls The stone handles on the front door are mostly or thoclase with minor amounts of pyro xene mica and o xide The feldspar is iridescent due to micro scopic planes of albite whic h act as a refraction grating The roc k is Larvikite an alk alic granitoid classifed as either syenite or monz onite quar ried in the Oslo Graben and cut and polished in Italy Gift from Edwin Eck el US Geological Surv e y Denv er Colorado and for mer e x ecutiv e secretary of the Society