Difference Between Fluorapatite and Hydroxyapatite

The key difference between fluorapatite and hydroxyapatite is that fluorapatite contains calcium phosphate in association with fluoride groups, whereas hydroxyapatite contains calcium phosphate in association with hydroxide groups.

Both fluorapatite and hydroxyapatite are phosphate-containing minerals. These are calcium phosphate forms containing different associated groups. That is, fluorapatite contains fluorine groups, while hydroxyapatite contains hydroxide groups.

1. Overview and Key Difference
2. What is Fluorapatite
3. What is Hydroxyapatite
4. Side by Side Comparison – Fluorapatite vs Hydroxyapatite in Tabular Form
5. Summary

What is Fluorapatite?

Fluorapatite or fluoroapatite is a phosphate mineral having the chemical formula Ca₅(PO₄)₃F. This mineral falls under the category of the apatite group. Also, it occurs as a hard, crystalline solid material that can have various colours, including green, brown, blue, yellow, violet, and sometimes the solid can be colourless. These colour variations arise due to the presence or absence of certain transition metal elements.

Difference Between Fluorapatite and Hydroxyapatite

Figure 01: Fluorapatite

Moreover, the crystal structure of fluorapatite is hexagonal. Also, the cleavage of this mineral is indistinct, and its fracture can be described as brittle or conchoidal. Furthermore, this mineral is considerably hard; Mohs hardness value is 5. And, it has a vitreous lustre with a white coloured mineral streak. Besides, this mineral is either transparent or opaque.

Among other phosphate minerals, fluorapatite is the most common and abundant phosphate mineral. We can find it in many igneous rocks. It can also occur in some biological systems. E.g. in the teeth of sharks and other fishes, in human teeth which have been exposed to fluoride ions in water, etc.

The production of fluorapatite can be done in a three-step process in addition to mining from the natural sources. At the first step, we need to generate calcium phosphate by combining calcium and phosphate salts. The pH is neutral here. Then, this material is reacted with fluoride sources to get the mineral. Finally, we can purify fluorapatite to remove any impurities.

There are many uses of fluorapatite. For example, the production of phosphoric acid, the production of hydrogen fluoride as a byproduct during the production of phosphoric acid, generation of fluorescence tube phosphors, as gemstone, etc.

What is Hydroxyapatite?

Hydroxyapatite is a phosphate mineral having the chemical formula Ca₅(PO₄)₃OH. It is an apatite group mineral. The hydroxide group of this material can be replaced with other groups such as fluoride group, chloride group, carbonate group, etc. The crystal system of this compound is hexagonal. The pure form of hydroxyapatite appears in white colour. But, the impurities can give it a range of colours, including grey, yellow, and yellowish-green colour.

Key Difference - Fluorapatite vs Hydroxyapatite

Figure 02: Hydroxyapatite

Furthermore, the fracture of this mineral is conchoidal, and it is brittle when a force is applied to it. The hardness of this mineral is similar to that of fluorapatite and the Mohs scale of hardness values 5. It has a vitreous lustre and a white mineral streak. Also, usually, hydroxyapatite is either transparent or translucent.

Besides, in addition to mining from natural sources, we can chemically synthesize hydroxyapatite via several methods. These methods include chemical deposition, biomimetic deposition, sol-gel process, and electrodeposition.

Moreover, there are several important uses of hydroxyapatite. These applications are mainly in the field of cosmetics, medicine and supplement production. In the field of cosmetics, hydroxyapatite is used in some variations of cornstarch-based baby powder. It is added as an emollient to help keep the moisture of the skin. In the field of medicine, hydroxyapatite is used for the formation of bone grafting materials. In the production of supplements, this mineral is used as a bone-building supplement with a superior absorption ability compared to calcium.

What is the Difference Between Fluorapatite and Hydroxyapatite?

The key difference between fluorapatite and hydroxyapatite is that fluorapatite contains calcium phosphate in association with fluoride groups, whereas hydroxyapatite contains calcium phosphate in association with hydroxide groups. Moreover, fluorapatite has various colours, including green, brown, blue, yellow, violet, and sometimes the solid can be colourless. But, the pure form of hydroxyapatite is white, but impurities can make it grey, yellow, or yellowish-green.

Below infographic shows more details regarding the difference between fluorapatite and hydroxyapatite.

Summary – Fluorapatite vs Hydroxyapatite

Both fluorapatite and hydroxyapatite are phosphate-containing minerals. The key difference between fluorapatite and hydroxyapatite is that fluorapatite contains calcium phosphate in association with fluoride groups, whereas hydroxyapatite contains calcium phosphate in association with hydroxide groups.

Reference:

1. “Hydroxylapatite.” Hydroxylapatite – an Overview | ScienceDirect Topics, Available here.
2. “Fluorapatite.” Wikipedia, Wikimedia Foundation, 22 Feb. 2020, Available here.
3. “Hydroxyapatite.” Wikipedia, Wikimedia Foundation, 8 Mar. 2020, Available here.