History:
A gatehouse is an entry control point building, enclosing or accompanying a gateway for a town, religious house, castle, manor house, or other fortification building of importance. At GZ, the gatehouse provided a stunning first impression for those visiting William Wyman’s estate in the 19th century. He owned much of the land that is now Homewood campus. He loved nature and he kept the grounds mostly undeveloped. The Two major buildings he established here where the villa, where he resided, and the gatehouse, also known as Homewood Lodge, which was the public entrance to his estate. After Wyman gave the land to John's Hopkins University in 1902, student groups met in this building. The Johns Hopkins newsletter made the gatehouse it's home in October 1965 and remains to this day
Construction:
Wyman, along with architect Louis Bucher, chose an the Italianate style for both buildings. In contrast to the wooden construction of the Villa, Wyman had the Gatehouse made of a green stone called serpentine.
Geology:
Serpentine is not the name of a single mineral. Instead it is a name used for a large group of minerals that fit this generalized formula: (X)2-3(Y)2O5(OH)4 In this formula, X will be one of the following metals: magnesium, iron, nickel, aluminum, zinc, or manganese; and, Y will be silicon, aluminum, or iron. The appropriate generalized formula is thus (Mg,Fe,Ni, Mn,Zn)2-3(Si,Al,Fe)2O5(OH)4. Chrysotile, antigorite, and lizardite are three of the primary serpentine minerals. There are many other serpentine minerals, most of which are rare. Serpentine group minerals have similar physical properties and form by similar processes. They often occur as fine-grained admixtures and can be difficult to distinguish within a rock. Geologists usually call these materials "serpentine" rather than more specific names to simplify communication.
Chemically, serpentine is a hydrated iron magnesium silicate. Serpentine rocks are high in iron and magnesium and low in sodium, potassium and calcium. They also may have high concentrations of nickel, cobalt and chromium. It is a metamorphic rock formed at tectonic plate boundaries where one plate is forced below another (subduction). Near the California coast where the Pacific plate dips under the North American plate, serpentine is common. It forms from the common rock peridotite when it comes in contact with seawater at low temperature and pressures.
Specifics of the Serpentine stone:
Serpentine is a very common mineral, and is found in abundance worldwide. Some famous localities include The Lizard Peninsula, Cornwall, England (the type locality of Lizardite; the Antigorio Valley, Piedmont, Italy (the type locality of Antigorite); and Mount Olympus, Cyprus. The Jeffery Asbestos Mine in Richmond Co., Quebec, is the one of the most productive asbestos mines, providing great amounts of Chrysotile. Thetford, in Megantic Co., Quebec has also produced fine Chrysotile. Serpentine is not a single mineral, but rather a group of related minerals. Besides for the main members of Antigorite and Chrysotile, a distinction is not usually made between the individual members except under scientific study and classification. Antigorite usually represents the more solid forms, and Chrysotile usually represents the fibrous forms, especially asbestos. Chrysotile is further sub-classified into four member minerals by its crystallization, and Clinochrysotile is by far the most prevalent form of Chrysotile. The subscripted 2-3 after the first set of elements denotes that there are two or three of the selected elements, depending on the charge of the element. Some very rare forms of Serpentine contain water [H2O] in place of the hydroxyl [OH]. Since the charge of water is different from hydroxyl, the formula of these rare forms is slightly altered. The two most common members of the Serpentine Group the dominate are: Antigorite - (Mg,Fe)3Si2O5(OH)4 Chrysotile - Mg3Si2O5(OH)4 Physical features of Antigorite: Antigorite is a mineral belonging to the serpentine group of minerals. Antigorite forms during low-grade metamorphism of olivine-rich rocks (peridotite and other ultrabasic rocks, gabbros, lamprophyres, etc.); is a major component in serpentinites. Antigorite can be accompanied by lizardite which can form the major component in pseudomorphs after orthopyroxene. Antigorite has a gridlike texture, where the fibres grow in two preferred orientations forming a grid. Physical Features of Chrysolite: Bulk chrysotile has a hardness similar to a human fingernail and is easily crumbled to fibrous strands composed of smaller bundles of fibrils. Naturally-occurring fibre bundles range in length from several millimetres to more than ten centimetres,[4] although industrially-processed chrysotile usually has shorter fibre bundles. Chrysolite is a soft, fibrous silicate mineral in the serpentine subgroup of phyllosilicates; as such, it is distinct from other asbestiform minerals in the amphibole group.
How It’s Used for Architecture:
Serpentine has been used as an architectural stone for thousands of years. It is available in a wide variety of green and greenish colors, often has an attractive pattern, works easily, and polishes to a nice luster. It has a Mohs hardness of 3 to 6 which is softer than granite, and usually harder than most marble. This low hardness limits its appropriate use to surfaces that will not receive abrasion or wear, such as facing stone, wall tiles, mantles, and window sills.
Logging the Cache:
Answer these questions and message me the answers:
- How has the weather affected the serpentine rocks?
- What is the texture of the serpentine rock?
- What is the predominate color of the rock at this location?
*Bonus
Take a photo of you and the Gatehouse
Sources:
https://geology.com/minerals/serpentine.shtml
https://ww2.kqed.org/quest/2010/08/05/learn-the-facts-about-serpentinite-before-its-removed-as-californias-state-rock/