A hand-held instrument enabling right angles to be set out accurately on a
site. Hammond
A type of twinning in quartz in which the parts of the twin are
alternately left- and right-handed. So named because it can be recognized
by optical tests in distinction to Dauphine (electrical) twinning. Optical
twinning as ordinarily applied includes all twin laws in quartz with the
exception of the Dauphine. Also called Brazil twinning; chiral twinning.
Am. Mineral., 2
The angle between the two optic axes of a biaxial crystal; its symbol is
2V (less than 90 degrees ), 2Valpha , or 2Vgamma ,
depending on whether the optic direction X or Z is in the acute bisectrix.
Syn:axial angle; optic-axial angle. CF:acute bisectrix;
obtuse bisectrix.
See:optic angle
A direction of single refraction in a doubly refracting mineral. Hexagonal
and tetragonal minerals have one such axis, and are termed uniaxial;
rhombic, monoclinic, and triclinic minerals have two optic axes and are
thus biaxial. See also:uniaxial; dispersion. CF:extinction
Anderson
The sub-field of physics that covers the behavior of light.
a. Indicates the type of double refraction in a mineral. In uniaxial
minerals, the material is said to be positive when the extraordinary ray
has a higher refractive index than the ordinary ray and negative when the
ordinary ray has the greater index. In biaxial minerals, which have three
basic optical directions, the refractive index of the intermediate or beta
ray is the criterion; if its refractive index is nearer that of the low or
alpha ray, it is said to be a positive mineral or stone; if it is nearer
the high or gamma ray, it is said to be a negative mineral or stone.
b. More technically, in uniaxial minerals, the material is positive when
the extreme refractive index (nepsilon ) is greater than the
apparently isotropic one (nomega ) and negative when the extreme
refractive index is less. In biaxial minerals, which have extreme
refractive indices both above and below the apparently isotropic one (n
beta ), the material is positive when the lower refractive index (n
alpha ) is closer to the apparently isotropic one and negative when
the higher one (ngamma ) is closer. Syn:optical sign;
optical character. See also:interference
Coordination of various processing factors, controls, and specifications
to provide best overall conditions for technical and/or economic
operation. Pryor, 4
That depth of cut required to completely fill the dipper in one pass
without undue crowding. Carson, 1
The water content at which a soil can be compacted to the maximum dry unit
weight by a given compactive effort. Also called optimum water content.
ASCE
a. A privilege secured by the payment of a certain consideration for the
purchase, or lease, of mining or other property, within a specified time,
or upon the fulfillment of certain conditions set forth in the contract.
b. S. Afr. The word option may refer to shares under option to the holder
of option certificates. In regard to mining activities, options are
granted to acquire the mineral rights and/or surface rights over some farm
at a price fixed in the agreement. This price may be a sum of money or a
participation in a mining company still to be formed. The option itself
can be acquired for a lump sum or for a payment of so much per morgen a
year. The option contract is generally connected with the permission for
the option holder to prospect for minerals and briefly referred to as
option and prospecting contract. Beerman
In coal preparation, optional-flow setups are those where coal usually
goes to the plant but can be diverted into storage, either in bins or
hoppers or on the ground. Coal Age, 3
Abbrev. for orthopyroxene. CF:cpx
An agreement to locate need not be in writing. If a party, in pursuance of
an oral agreement to locate at the expense of another, locates the claim
in his or her own name, he or she holds the legal title to the ground in
trust for the benefit of the party for whom the location was made. Such a
party could, upon making the necessary proofs, compel the locator of the
mining claim to convey the title to him or her, although the agreement to
do so was not in writing. Such an agreement is not within the statute of
frauds. Ricketts
A division of the color scale, generally given as about 900 degrees C.
A variant of the clamshell bucket with four or five leaves instead of the
clamshell's two. Each leaf ends in a reinforced point. Its digging ability
is less than that of the clamshell, and its principal use is for
underwater excavation and digging. Carson, 1
An apparatus consisting of four movable jaws that converge to a point when
closed; used to obtain samples of underwater sediment. AGI
Adj. Describes rounded to spherical, commonly banded, textures within
minerals or rocks; e.g., orbicular diorite.
A structure developed in certain phanerocrystalline rocks (e.g., granite
and diorite) due to the occurrence of numerous orbicules.
Syn:spheroidal structure; nodular structure.
A hexagonal mineral, Ni5-x As2 ; rose-bronze; at the
Tiebaghe massif, New Caledonia.
A condition when atoms in a solid solution arrange themselves in regular
or preferential positions in the lattice, rather than at random.
Newton, 1