<![CDATA[1A Collections]]> https://wserv3.esc.cam.ac.uk/p1acollections/items/browse?page=3&output=rss2 Tue, 09 Apr 2024 21:16:53 +0100 p1acollections@esc.cam.ac.uk (1A Collections) Zend_Feed http://blogs.law.harvard.edu/tech/rss <![CDATA[Resinous [lustre]]]> https://wserv3.esc.cam.ac.uk/p1acollections/items/show/249

Title

Resinous [lustre]

Subject

Minerals displaying the lustre of resin or of smooth-surfaced plastic are described as resinous. Amber, for example, has resinous lustre.

]]> Fri, 21 Jun 2019 17:29:48 +0100 <![CDATA[Replacement]]> https://wserv3.esc.cam.ac.uk/p1acollections/items/show/248

Title

Replacement

Subject

An igneous texture in which a mineral grain is resorbed and a later crystallising phase grows in its place.
]]> Fri, 21 Jun 2019 17:29:09 +0100 <![CDATA[Relief]]> https://wserv3.esc.cam.ac.uk/p1acollections/items/show/247

Title

Relief

Subject

When viewed under plane polarised light, some mineral grains are more clearly defined than others. They have heavier, darker edges. These minerals have higher relief.

Relief is determined by the difference in the refractive indices of the grain and mounting medium. The mounting medium typically has a refractive index (R.I., ni) of ~1.54. A mineral with a low refractive index, such as quartz (R.I., ni ~1.5) has low relief because it has a refractive index very similar to that of the mounting medium. A mineral with a high refractive index, such as garnet (R.I., ni ~1.7) has high relief because it has a refractive index much higher than that of the mounting medium.

]]> Fri, 21 Jun 2019 17:28:37 +0100 <![CDATA[Prismatic]]> https://wserv3.esc.cam.ac.uk/p1acollections/items/show/246

Title

Prismatic

Subject

An elongate “pencil-like” crystal habit. Prismatic crystals are wider than acicular crystals.
]]> Fri, 21 Jun 2019 17:26:28 +0100 <![CDATA[Porphyroblast]]> https://wserv3.esc.cam.ac.uk/p1acollections/items/show/245

Title

Porphyroblast

Subject

A porphyroblast is the metamorphic equivalent of a phenocryst. Do not confuse them! It is a large crystal set into a finer-grained fabric, in a metamorphic rock.

Description

Compare with phenocryst.

]]> Fri, 21 Jun 2019 17:25:55 +0100 <![CDATA[Porphyritic]]> https://wserv3.esc.cam.ac.uk/p1acollections/items/show/244

Title

Porphyritic

Subject

An igneous rock containing phenocrysts in a fine-grained groundmass is said to have a porphyritic texture.

]]> Fri, 21 Jun 2019 17:25:05 +0100 <![CDATA[Porosity]]> https://wserv3.esc.cam.ac.uk/p1acollections/items/show/243

Title

Porosity

Subject

The proportion of the material occupied by space, measured in volume percent. A porous material contains fluid-filled spaces, or pores, while a non-porous material does not. NB, make sure you understand the difference between porosity and permeability.

Description

Compare with permeability.

]]> Fri, 21 Jun 2019 17:17:25 +0100 <![CDATA[Polycrystalline]]> https://wserv3.esc.cam.ac.uk/p1acollections/items/show/242

Title

Polycrystalline

Subject

A crystalline sample of a single mineral, containing many crystals. Quartzite, for example, is polycrystalline quartz.

Description

Have a look at the quartzites (L520, L521) in the 1A Reference Series.
]]> Fri, 21 Jun 2019 17:15:36 +0100 <![CDATA[Poikilitic]]> https://wserv3.esc.cam.ac.uk/p1acollections/items/show/241

Title

Poikilitic

Subject

An igneous texture in which a small number of large grains enclose many smaller grains of another phase.

Description

Have a look at the gabbro (L141) in the 1A Reference Series.
]]> Fri, 21 Jun 2019 17:11:22 +0100 <![CDATA[Plutonic]]> https://wserv3.esc.cam.ac.uk/p1acollections/items/show/240

Title

Plutonic

Subject

Plutonic rocks and textures are those associated with deep magmatic intrusions, where cooling is slow. Crystals are thus able to grow very large, producing coarse-grained textures. This term is restricted to large igneous bodies more than hundreds of metres in diameter.
]]> Fri, 21 Jun 2019 17:09:36 +0100