Lab 9: Minerals and Mineral Identification

Flashcards covering physical properties of minerals (luster, streak, hardness, crystal form, cleavage, fracture, acid reaction, and magnetism) and visual identification of common minerals.

What is the scientific definition of a mineral?

A mineral is a naturally occurring inorganic solid with a definite chemical composition and an orderly crystalline structure.

What is mineral luster, and what is its broadest division?

Luster is the appearance of light reflected from a specimen's surface, and its broadest division is between metallic luster and non-metallic luster.

How does streak distinguish metallic minerals from non-metallic minerals?

Metallic minerals always leave a dark streak, whereas non-metallic minerals always leave a light streak.

Which specific colors categorize a non-metallic mineral as dark colored?

A non-metallic mineral is considered dark colored if it is black, dark gray, brown, dark green, or dark red.

What underlying factor causes differences in hardness among minerals?

Differences in hardness arise because the bonds holding the atoms together in the minerals have different strengths.

What are the softest and hardest reference minerals on Mohs Hardness Scale, and what are their numbers?

Talc is the softest mineral with a hardness of $1$, and diamond is the hardest mineral with a hardness of $10$.

What are the hardness values for a fingernail, a copper-coated penny, and a piece of glass?

A fingernail has a hardness of about $2.5$, a copper-coated penny has a hardness of about $3.5$, and a piece of glass has a hardness of about $5.5$.

What is the hardness of quartz on Mohs Hardness Scale, and can it scratch glass?

Quartz has a hardness of $7$, which means it can scratch glass (hardness of about $5.5$).

What tool is used to test a mineral's powdered form, and what is its hardness threshold?

A small ceramic tile called a streak plate is used; minerals harder than about $6.5$ to $7$ will not leave a streak on it.

On which type of specimens should the streak test be performed?

The streak test should only be done for opaque specimens (those that do not let light through), and not on transparent or translucent specimens.

What color streak does the dark-colored mineral sphalerite leave?

Sphalerite leaves a light-colored streak that ranges from white to yellowish-brown.

How do the crystal forms of quartz and halite differ?

Quartz crystals form six sides ending with a point, whereas halite crystals are cube-like with six sides and $90^\circ$ corners and edges.

What causes mineral cleavage, and how does it appear in transparent specimens?

Cleavage occurs because chemical bonds are weaker along certain planes in the crystalline structure, appearing as fractures running parallel to the surface of the crystal.

What cleavage characteristic is demonstrated by biotite mica?

Biotite mica has good cleavage in one direction, allowing it to easily split into thin sheets.

What is conchoidal fracture?

Conchoidal fracture is a type of mineral fracture where the specimen breaks smoothly with curved surfaces, like glass breaks.

What reaction occurs when dilute hydrochloric acid is placed on minerals containing calcium carbonate ($CaCO_3$)?

The acid causes minerals composed of calcium carbonate ($CaCO_3$) to effervesce (fizz).

Which two calcium carbonate minerals effervesce with dilute acid, and which similar-looking minerals do not?

Calcite and aragonite effervesce with dilute hydrochloric acid, while halite and quartz do not.

How does a magnetic mineral interact with a compass needle?

A magnetic mineral can attract or deflect the needle of a compass, pulling it away from north.

What are the key diagnostic properties of calcite identified by sight?

Calcite is usually colorless, white, or yellow, often forms rhombohedral crystals, has non-cubic cleavage, and has crystal corners with $75^\circ$ angles.

What are the key diagnostic properties of halite identified by sight?

Halite is usually colorless to white, often forms cubic crystals with cubic cleavage, and has crystal corners with $90^\circ$ angles.

What are the key diagnostic properties of pyrite identified by sight?

Pyrite is usually brass-yellow in color, often forms cubic crystals, and has crystal corners with $90^\circ$ angles.

What are the key diagnostic properties of galena identified by sight?

Galena is usually silver/gray in color, often forms cubic crystals with cubic cleavage, and has crystal corners with $90^\circ$ angles.